In short. An inductive sensor equivalent is selected on five fields: housing diameter, installation type, assured range on your metal, output type, connection method. The range is not the catalogue Sn but Sn × 0.81 × your metal's factor from that specific model's datasheet × a 0.8 margin, or the datasheet Sa where the manufacturer prints one, and the result has to exceed the actual gap in the assembly. The worked material is below: five examples of an original and our item, and the catalogue tables for M8, M12, M18, M30 and block housings.
The five fields that decide a replacement
An equivalent inductive sensor matches the original on five parameters, and the order matters: housing diameter, installation type (shielded or unshielded), assured sensing zone on your metal, output type, connection method. Matched the first and the fourth but skipped the second and third? The sensor will screw into the bracket and never see the target. That is the most common way to get this wrong.
Below are three things that derail a replacement. The sensing-range figure does not mean what most people assume. Shielded and unshielded are not interchangeable, and the reverse rule of thumb that "unshielded reaches twice as far" holds on far fewer models than people think. Output type drags the cabinet into the job, not just the sensor. Every figure in this article comes from a manufacturer datasheet, and we can quote the document number on request.
Argument one: the catalogue Sn is not what you size against
Catalogues list the rated sensing range Sn. IEC 60947-5-2 calls it a conventional quantity. Clause 2.3.1.1 states it plainly: the rated operating distance does not take into account either manufacturing tolerances or variations due to external conditions such as voltage and temperature. What gets measured instead is the effective range sr, and the standard only requires it to fall between 0.9 and 1.1 Sn at rated voltage and 23 °C (clause 7.2.1.3.1).
Measurement uses a standard target, and clause 8.3.2.1.1 defines its size: a square of carbon steel Fe 360, 1 mm thick, rolled finish. The side length equals the diameter of the circle inscribed on the active surface of the sensing face, or three times Sn, whichever is greater. Note the wording: the target side is set by the inscribed circle of the sensing face, not by the housing thread. Your actual part rarely resembles that target in either size or shape.
The figure you design the mounting against is a different one: the assured operating distance Sa, which the standard defines as a range from zero to 0.81 Sn (clause 7.2.1.3.3). A range, deliberately, and the zero lower bound comes from the standard rather than from any datasheet. Manufacturers write it down differently. Pepperl+Fuchs prints the fork: NBB5-18GM50-E2 gives sa 0…4.05 mm at sn 5 mm, NBB20-U1-UU gives sa 0…16.2 mm at sn 20 mm. Sick and Balluff print a single figure, the upper bound: on IME12-04BPSZC0K the row reads "Safe sensing range Sa 3.24 mm" at Sn 4 mm, on IQ40-40NPPKC0K Sa 32.4 mm at Sn 40 mm, on Balluff BES008F Sa 6.4 mm at Sn 8 mm. The "0…X" notation appears in none of the Sick datasheets we checked. The practical conclusion: if the manufacturer prints Sa, size against it, and use the 0.81·Sn formula only when the datasheet gives no Sa. On BES008F the datasheet 6.4 mm is 0.80 Sn, so the formula would have overstated the range by 0.08 mm.
The effective range also has spread. The NBB20-U1-UU datasheet states sr as 18…22 mm at a nominal 20, NBN40-L2-A2-V1 as 36…44 mm at a nominal 40, NJ4-12GM40-E2-5M as 3.6…4.4 mm at a nominal 4.
Two figures the catalogue never shows
The first is hysteresis. The release distance is always longer than the operate distance, and manufacturers specify that gap very differently. Sick states 5…15 % of sr for the IME series, 3…20 % for the hygienic IMF, 3…15 % for the block-shaped IQ40, and 2…10 % for the older IM Standard series. Pepperl+Fuchs gives typically 5 % for the NBB and NBN series, 1…10 % with 3 % typical for the stainless NJ, and 1…10 % with 5 % typical for NBB20-U1-UU. Omron writes "10 % max. of sensing distance" for E2A. Balluff BES M18MI-PSC80B-BV03 states up to 15 % of sr. SELET series B60 specifies hysteresis as a percentage of Sn rather than sr, and gives under 10 %. The standard itself allows up to 20 % of sr (clause 7.2.1.5), so all of the above are within limits, yet the spread between them is twofold.
The second is temperature drift. Sick prints it on its own row: ±10 % of sr in the IME, IMF and IQ40 datasheets. Balluff states up to 15 % of sr for BES008F. Omron gives ±10 % of sensing distance over −25 to +70 °C and ±15 % over −40 to +70 °C. Pepperl+Fuchs has no separate drift row in its datasheets: the manufacturer points to the usable range su, which the standard defines as 0.9…1.1 sr across the whole ambient temperature range and at 85 to 110 % of rated supply voltage (clause 7.2.1.3.2). So ±10 % of sr at P+F is not a separate specification but a consequence of that band.
One telling case: the NBB5-18GM40-Z0-V1 datasheet prints two Sa values, 0…4.05 mm over −25 to +70 °C and 0…3.8 mm over −40 to −25 °C. In the cold the assured zone drops by 6 %, and the manufacturer documents that rather than leaving it to guesswork.
The margin we recommend
Our working rule: keep the actual gap in the assembly no larger than 0.8 of Sa calculated for your metal. Sa already covers voltage and temperature, but it does not cover vibration, bracket play, a target smaller than the standard one, or the hysteresis spread itself, which reaches 15…20 % on some models. A 20 % margin is there precisely for that. Omron, incidentally, puts its own limit in roughly the same place. It does not print Sa: the E2A datasheet carries a Setting distance row in millimetres, and at Sn 8 mm it reads "0 to 6.4 mm". The 0.8 ratio holds in every column of that table (0…1.6 at Sn 2; 0…3.2 at Sn 4; 0…6.4 at Sn 8; 0…12 at Sn 15), but the formula 0.8·Sn is nowhere in the datasheet; that arithmetic is ours.
The material factor is a property of the model, not a physical constant
On steel the factor is one; on non-ferrous metals the zone drops several times over. Indicative figures from Sick IME datasheets: stainless V2A/304 around 0.8, aluminium 0.45, copper 0.4, brass 0.4. For the hygienic IMF the manufacturer gives different ones: stainless 0.74, copper 0.33, brass 0.46. For the block-shaped IQ40 different again: stainless 0.8, aluminium 0.34, copper 0.27, brass 0.38. For the older IM08-1B5PS-ZT1: stainless V4A 0.78, aluminium 0.38, copper 0.29, brass 0.49.
At Pepperl+Fuchs the model-to-model spread is wider still. NJ2-12GM40-E2 drops to 0.23 on aluminium and 0.21 on copper. NBB2-12GM50-E2-V1 gives 0.29 and 0.23. NBN4-12GM50-E2-V1 already gives 0.47 and 0.43, and 0.85 on stainless. NBB10-30GM50-E2-V1 gives 0.50 on aluminium. Between two sensors from the same manufacturer the aluminium factor differs by more than a factor of two.
The clearest illustration of why a generic table fails: NBB5-18GM50-E2 has two datasheets. The current document gives 0.35 on aluminium, 0.29 on copper and 0.73 on stainless. The 2020 datasheet for the same part number gives 0.30, 0.30 and 0.70, plus a different supply voltage. You can tell a unit apart by its housing finish: nickel means the older revision, white bronze means the current one. One part number, two sets of figures.
Omron does not publish a factor table for E2A at all. In its place the datasheet carries "Influence of Sensing Object Size and Materials" curves for iron, stainless SUS303, brass, aluminium and copper. We will not read a value off a curve and print it as a factor: that is an estimate, not a datasheet figure. Balluff and SELET do not print factors in their documents either.
Take the figure from the datasheet of the model you are buying. That is what we do on every enquiry: open the datasheet for the specific part number, read the correction-factor row for the metal in question, and only then say whether the item will cover your gap.
The working calculation, with two examples
The sequence: multiply Sn by 0.81, then by your metal's factor from that specific model's datasheet, then by a 0.8 margin. The result must exceed the actual gap in the assembly at the worst position of the mechanism.
Example one. M18 housing flush with a plate, target in stainless steel 304, gap 3 mm. NBB5-18GM50-E2-V1: 5 × 0.81 × 0.73 × 0.8 = 2.37 mm. Fails. NBB8-18GM50-E2-V1: 8 × 0.81 × 0.74 × 0.8 = 3.84 mm. Passes with 0.84 mm to spare. Of the two shielded M18 options in the catalogue only the 8 mm one works, even though by eye a 5 mm sensor looks ample for a 3 mm gap.
Example two, aluminium. M12 housing, flush. NBB4-12GM50-E2-V1 with Sn 4 mm and a factor of 0.40 gives 4 × 0.81 × 0.40 × 0.8 = 1.04 mm. NBN4-12GM50-E2-V1 at the same Sn 4 mm gives 1.22 mm, because its aluminium factor is 0.47. The stainless NJ2-12GM40-E2 with Sn 2 mm and a factor of 0.23 gives 0.30 mm, meaning it barely works on aluminium at all. This multiplier is exactly why aluminium and copper replacements fail most often: in the catalogue the item looks like a fourfold margin on the gap, and after three multiplications you are left with a millimetre that does not exist in a real assembly with vibration and thermal expansion.
Argument two: shielded and unshielded are not interchangeable
A shielded sensor (flush) has metal shielding around its side surface. It can be sunk into a metal boss level with the surface. An unshielded one (non-flush) cannot be mounted that way: the metal around the face reads as a target and the sensor latches on permanently. These arrive at us for testing as "faulty" regularly, and every time it turns out an unshielded equivalent was in the store, someone screwed it into the same boss in place of the shielded part, and the assembly has not produced a correct signal since.
Why "unshielded reaches twice as far" misleads
That rule describes typical product lines, not specific part numbers. Pepperl+Fuchs states it in its own blog as "flush gives about 60 % of the switching distance of non-flush" and calls it a guideline itself. Check the model.
Where the rule holds. Omron E2A per the official table: M8 gives 2 mm shielded and 4 unshielded, M12 gives 4 and 8, M18 gives 8 and 16. At M30 it already breaks: shielded 15 mm, while unshielded is 20 mm in the standard K body and 30 mm in the long L body. SELET series B60: M12 2 and 4, M18 5 and 8, M30 10 and 15, so at M30 the ratio is one and a half, not two. At Sick the rule holds on M8: IME08-02BPSZT0K shielded at 2 mm, IME08-04NPSZT0K unshielded at 4 mm.
Where the rule fails. NBB8-18GM50-E2-V1 shielded and NBN8-18GM50-E2-V1 unshielded sit on the same M18×1 thread with the same Sn 8 mm and the same Sa 0…6.48 mm. Same on M12: NBB4-12GM50-E2-V1 and NBN4-12GM50-E2-V1 are both 4 mm with Sa 0…3.24 mm. At Sick on M12, IME12-04BPSZC0K flush and IME12-04NPSZC0S non-flush are also both 4 mm. Balluff BES008F is shielded at 8 mm in an M18 housing, and the manufacturer's footnote points to a separate mounting guide for shielded sensors with extended range.
The reason is simple. Manufacturers build two different shielded designs: standard and extended-range. For M18 at Pepperl+Fuchs the standard shielded part is NBB5 at 5 mm, while NBB8 at 8 mm is already the extended-range design. Compare two specific items on Sn and Sa, not "flush versus non-flush".
What the unshielded part does give you at the same range: better non-ferrous factors and a higher switching frequency. In the NBN8 versus NBB8 pair, on the current datasheets, aluminium is 0.44 against 0.38, copper 0.42 against 0.35, brass 0.52 against 0.47, frequency 1650 Hz against 1350. On the 2020 revisions the gap is different: copper is 0.4 on both and the frequency is 500 Hz on both. So the choice between them comes down to the target metal and speed, not range.
Two practical consequences still stand:
- Swapping shielded for unshielded without changing the mounting gives permanent switching. Either free the metal around the face or buy shielded.
- Swapping unshielded for shielded may cut the range, or may not. Check Sn and Sa on both items, and if the range really does drop, either increase the housing diameter or reduce the gap.
In the Sick code the installation reads directly: in IME12-04BPSZC0K the letter B means embeddable, in IME12-04NPSZC0S the letter N means non-flush, and the digits before the letter are Sn in millimetres. Pepperl+Fuchs follows the same logic: NBB is shielded, NBN is unshielded, and the number after the letters is Sn.
Argument three: the output and the wires change the cabinet, not just the sensor
Keep the output type unless you are ready to rework the circuit. Four cases where a "similar" sensor will not do.
- PNP instead of NPN and vice versa. The controller input is configured for one type. Swapping the sensor without reconfiguring the input means no signal. How to establish which one you have is covered in how to test a proximity sensor with a multimeter. In short: apply power, measure the voltage between the output and the negative rail, bring metal close. Supply positive appearing at the output means PNP; the output pulling down to negative means NPN. For VFD inputs the reconfiguration procedure is in replacing a European drive with Veichi.
- Complementary instead of single-output. Suffix A2 at Pepperl+Fuchs, B3 at Omron, and a second P in the Sick code (as in IQ40-40NPPKC0K) all mean a four-wire scheme with both outputs live at once: normally open and normally closed on separate terminals. Such a sensor will not replace a three-wire part in an existing three-core cable, because there is nothing to carry the second output.
- Two-wire instead of three-wire. A two-wire sensor is wired in series with the load, and it is constrained in both directions. Off-state residual current: up to 1.5 mA on NBB20-U1-UU, which a sensitive PLC input can read as an on state. Minimum operating current: 5 mA on that same NBB20-U1-UU and 2 mA on NBB5-18GM40-Z0-V1, so the load must draw at least that much or the sensor will not switch.
- Different voltage and an entirely different circuit. Detailed below.
Why NBB20-U1-UU is not a replacement for a 24 V sensor
Most catalogue items are three-wire sensors at 6…36 or 10…30 V DC. NBB20-U1-UU sits apart: it is a two-wire sensor for AC and DC. The datasheet gives a rated operating voltage of Ue 24…250 V DC or 24…230 V AC, with the permissible range UB 20…275 V DC and 20…253 V AC on a separate row. It cannot be fitted in place of a 24 V sensor, and here is why.
A two-wire sensor is wired in series with the load, not in parallel. It has no separate negative; its supply passes through the load itself. Hence four hard conditions from the same datasheet: voltage drop Ud up to 5 V in DC operation and up to 8 V in AC operation (2 and 3 V typical), minimum operating current Im 5 mA, load current IL from 5 to 500 mA, residual off-state current Ir up to 1.5 mA. Plus an explicit requirement: the device shall be protected by an external fuse in accordance with UL 248, rated 3 A and suitable for 300 V AC and DC. It connects through a terminal compartment for 0.5…2.5 mm² conductors at 1.2 Nm, not through a plug.
So this is not a sensor swap but a circuit-section swap: different wiring topology, different load, an external fuse, terminals instead of a connector. Its output polarity is set by the wiring itself, as the datasheet puts it: "normally open/closed selectable through wiring". People choose it deliberately, when a contactor coil has to be switched straight off the mains without an interposing relay.
The detail that stops an installation for an hour
The connection method, and not just plug versus cable. Pin counts differ too. NBB8-18GM50-E2-V1 and NBB2-12GM50-E2-V1 are M12 with three pins, while NBN40-L2-A2-V1 is M12 with four, because it is four-wire. At Sick the IME08 series uses an M8 connector with three pins while IME12 uses an M12 with four, even though the sensor itself is three-wire. At Omron the M1 suffix always means an M12 connector with four pins, even on three-wire B1 and B2 parts.
Physically, A-coded M12 connectors with three and four pins are compatible: a three-pin sensor simply leaves pin 2 unused. The problem is not there but on four-wire sensors: two outputs cannot travel down a three-core cable. Cable length is a compatibility field as well: NJ4-12GM40-E2-5M has a moulded 5 m cable, Balluff BES008F 3 m, most P+F and Omron parts 2 m. And NBB15-U1-E2 and NBB20-U1-UU have no cable at all: they have a terminal compartment and you run your own.
The catalogue lists both variants of one item: NBB5-18GM50-E2 with a 2 m cable and NBB5-18GM50-E2-V1 for an M12 plug. Same with the pair NBN4-12GM50-E2 (cable) and NBN4-12GM50-E2-V1 (plug).
How to read a part number
Some of the compatibility fields are visible straight from the marking, without a datasheet.
| Brand | What it tells you | Example |
|---|---|---|
| Sick IME / IMF / IM / IQ | family and thread, then Sn in mm, then installation (B = embeddable, N = non-flush), then output (P = PNP, N = NPN), then function (S = normally open, O = normally closed, P = complementary) | IME12-04BPSZC0K: M12, Sn 4 mm, shielded, PNP, normally open |
| Pepperl+Fuchs NBB / NBN | NBB = shielded, NBN = unshielded; the number after the letters = Sn in mm; the 8GM / 12GM / 18GM / 30GM element = housing thread; L2 and U1 = not a barrel but a block and a flanged body | NBN8-18GM50-E2-V1: unshielded, Sn 8 mm, M18, plug |
| P+F output suffixes | E2 = PNP normally open, E3 = PNP normally closed, E0 = NPN normally open, E1 = NPN normally closed, E4 and E5 = NO/NC switchable, A0 and A2 = four-wire complementary (NPN and PNP), Z0 = two-wire DC, UU = universal AC/DC with the logic chosen by wiring, V1 = M12 plug, 5M = 5 m cable | NBB20-L2-A2-V1: four-wire PNP, NO and NC outputs at once, M12 plug with 4 pins |
| Omron E2A | M or S after E2A = brass or stainless steel, then the diameter, then K or L = standard or long body, then S or N = shielded or unshielded, then Sn in mm. Suffixes: M1 = M12 plug with 4 pins, WP = moulded PVC cable (length as a separate suffix such as 2M), B1 = PNP normally open, B2 = PNP normally closed, B3 = PNP four-wire with two outputs, C1/C2/C3 = the same in NPN | E2A-M18LS08-M1-B3: M18, long body, shielded, Sn 8 mm, M12 plug, two outputs |
| SELET B60 / B61 | B60 = Cenelec series, B61 = short series; nothing in the installation position = shielded, E = unshielded; then the diameter, then the sensing distance; P = PNP, N = NPN; O = normally open, C = normally closed; C5 = M12 connector, nothing = cable, G = cable output | B60122POC5: M12, shielded, Sn 2 mm, PNP, normally open, M12 connector |
Four traps inside the codes themselves
At Sick the letter B does not always mean fully flush. It covers quasi-flush as well, so the installation type is settled by the datasheet, not the letter. IME08-03BPSZW2S, for instance, is listed as Quasi-flush.
In the form 1B5 the letter B is a decimal point, not an installation code. IME08-1B5PSZT0S has Sn 1.5 mm. Same with 2B5: IMM05-2B5PSVR8K has Sn 2.5 mm.
At Pepperl+Fuchs the NJ prefix encodes no installation type at all. The manufacturer sells NJ in both versions: NJ2-12GM40-E2 is flush at 2 mm, while NJ4-12GM40-E2-5M is non-flush at 4 mm. Both come in a 1.4305 stainless housing. For NJ, check the installation type in the datasheet only.
At Omron the letter M in the shielding position is not valid. That position accepts only S or N. If an E2A code with an M in sixth position lands in your enquiry, it is either a supplier typo or a mis-transcribed nameplate, and it needs a question before an order. Omron's own datasheets are not flawless either: in the D03E ordering table the M18LN16 row prints its B3 column as E2A-M18LS16-M1-B3, with the wrong shielding letter. In the text layer of the D03E ordering table such S/N shielding-letter typos occur in several rows of the B3/C3 columns, and this is one example.
What the marking does not tell you and always needs the datasheet for: the assured zone Sa, the non-ferrous correction factors, switching frequency, enclosure rating, permissible load current, and the connector pin count. Omron's M1 and WP suffixes, incidentally, say nothing about ingress protection either: IP67 after IEC 60529 and IP69k after DIN 40050 appear on their own row.
A note on the Sick series. IME is the industrial standard: nickel-plated brass housing, IP67, −25 to +75 °C, two mounting nuts supplied. IMF is the hygienic series for food and wet areas: V4A stainless to DIN 1.4404 / AISI 316L, IP68 with an IP69K footnote, −40 to +100 °C, stainless nuts as well. If the replacement is going onto a line with pressure washdown, the difference between these two series matters more than matching Sn.
Five worked examples: the original and our item
Real five-field calculations below. The original part numbers are verified in the manufacturers' official catalogues, our items in Sick and Pepperl+Fuchs datasheets. Where the match is not complete, we say exactly which field does not match.
1. Omron E2A-M12KS04-WP-B1 2M
Original: M12, shielded, Sn 4 mm ±10 %, PNP normally open, three-wire, moulded PVC cable 2 m, supply 12…24 V, frequency 1000 Hz.
Our item: Sick IME12-04BPSZC0K. M12 diameter matches. Flush installation matches. Range Sn 4 mm and Sa 3.24 mm. PNP normally open output matches. Supply 10…30 V covers 12…24 V. One field does not match: the connection. Ours is an M12 plug with 4 pins, the original has a moulded cable. Fix: add an M12 cordset (P+F V1-W-5M-PUR, 4 pins, PUR, 5 m; other lengths supplied on request), or take P+F NBN4-12GM50-E2 with a moulded 2 m cable, but that one is unshielded, so the boss has to be freed. There is currently no cable version of a shielded M12 at 4 mm in the catalogue, and that is worth knowing before ordering.
On the metal side: Sick IME gives stainless 0.8 and aluminium 0.45, so steel has full margin, and aluminium gives 4 × 0.81 × 0.45 × 0.8 = 1.17 mm of assured gap.
2. Omron E2A-M18LN16-M1-B1
Original: M18, unshielded, Sn 16 mm ±10 %, PNP normally open, three-wire, M12 plug with 4 pins, frequency 400 Hz.
Our item: there is no direct equivalent, and that needs saying out loud. The longest unshielded M18 in the catalogue is NBN8-18GM50-E2-V1, Sn 8 mm, Sa 0…6.48 mm. On steel that gives 6.48 × 0.8 = 5.18 mm of working gap.
So measure the actual gap first rather than copying the original's Sn. If the real gap is up to 5.1 mm on steel, NBN8-18GM50-E2-V1 closes the job and the bracket stays untouched. If it is longer, the M18 thread has to go: from the catalogue the options are NBB20-L2-E2-V1 (L2 block, Sn 20 mm, Sa 0…16.2 mm, shielded, PNP normally open, three-wire, M12 plug) or NBN40-L2-A2-V1 (Sn 40 mm, unshielded). The second is four-wire complementary, so the cable changes too. The L2 body does not screw into an M18 boss, it is a block on two bolts, so bracket rework is mandatory either way.
3. SELET B60E188POC5
Original: M18, unshielded, Sn 8 mm, PNP normally open, M12 connector, supply 12…24 V, hysteresis under 10 % of Sn, IP67, −25 to +60 °C, frequency 700 Hz.
Our item: P+F NBN8-18GM50-E2-V1. All five fields match: M18, unshielded, Sn 8 mm (ours also states Sa, 0…6.48 mm), PNP normally open three-wire, M12 plug. Two fields are better on ours: supply 6…36 V against 12…24, and temperature −40 to +85 °C against −25 to +60. Frequency: on the current datasheet revision 1650 Hz against the original's 700; on the 2020 revision the same part number gives 500 Hz, below the original. We confirm the revision of the batch before shipping. And our factors are in the datasheet: aluminium 0.44, copper 0.42, stainless 0.76, brass 0.52.
4. SELET B603010POC5
Original: M30, shielded, Sn 10 mm, PNP normally open, M12 connector, supply 12…24 V, frequency 200 Hz.
Our item: P+F NBB10-30GM50-E2-V1. M30×1.5 thread, flush, Sn 10 mm, Sa 0…8.1 mm, PNP normally open three-wire, M12 plug with 3 pins, supply 6…36 V. Five fields out of five. Frequency 1100 Hz against 200, so ample speed margin. On aluminium, 10 × 0.81 × 0.50 × 0.8 = 3.24 mm of assured gap, which is a normal working mounting for M30.
5. SELET B60G185PO
Original: M18, shielded, Sn 5 mm, PNP normally open, moulded cable, supply 12…24 V.
Our item: P+F NBB5-18GM50-E2. M18, flush, Sn 5 mm, Sa 0…4.05 mm, PNP normally open, moulded 2 m cable, supply 6…36 V per the current datasheet. Five out of five, right down to the connection type.
One caveat specific to this item: NBB5-18GM50-E2 has two datasheets with different data. The current one gives 6…36 V and factors 0.35 / 0.29 / 0.73; the 2020 legacy one gives 10…30 V and 0.30 / 0.30 / 0.70. If your calculation is tight on aluminium, write to us and we will state the revision of the batch we are shipping.
What the catalogue holds, by housing size
The range is given as rated Sn. Sa is shown where the manufacturer prints it, in the form the manufacturer uses: a fork from zero for Pepperl+Fuchs, a single upper-bound figure for Sick and Balluff. To size a mounting, multiply Sn by 0.81, by your metal's factor from that model's datasheet, and by a 0.8 margin. The items below are published in the catalogue; availability and lead time are confirmed per enquiry, because some brands in this group are already discontinued.
One P+F part number can come with two datasheet revisions
Pepperl+Fuchs reissued the datasheets for its inductive sensors, and some numeric rows differ between the new revision and the old one. The part number stays the same. We cross-checked four pairs of documents:
- NBB8-18GM50-E2-V1: the 2020 revision (doc. 085501) gives 500 Hz, an M12 plug with 4 pins, factors of 0.45 aluminium, 0.4 copper, 0.7 stainless 304, a 10…30 V supply and a separate "Increased operating distance" line. The current revision (doc. 326161-0087) gives 1350 Hz, 3 pins, copper 0.35, and no longer carries that line.
- NBN8-18GM50-E2-V1: the 2020 revision (doc. 084197) gives 500 Hz, 4 pins, aluminium 0.5, copper 0.4, stainless 0.7. The current one (doc. 326161-0120) gives 1650 Hz, 3 pins, copper 0.42 and a −40 to +85 °C range.
- NBN4-12GM50-E2-V1: the older documents 083960 (2009) and 087768 (2020) give 1200 Hz and a 10…30 V supply; the current revision 326161-0069 gives 6…36 V and a 3-pin plug. On the pin count in the legacy pair: 087768 prints a "Connector M12 x 1, 4-pin" row, while 083960 does not print a pin count at all ("V1-connector") and its four cores are only visible in the connection table.
- NBB5-18GM50-E2: the 2020 datasheet (doc. 083995) gives a 10…30 V supply, 800 Hz and factors of 0.30 aluminium, 0.30 copper, 0.70 stainless; the current one (doc. 326161-0105) gives 6…36 V, 1950 Hz and 0.35 / 0.29 / 0.73.
Sa and sr are identical in both revisions, so the split does not affect sizing by distance. But if your assembly is tight on switching frequency, connector pin count or supply limits, we confirm the revision of the actual batch before shipping instead of quoting one datasheet as final.
M8
| Item | Sn / Sa | Installation | Output | Connection |
|---|---|---|---|---|
| Sick IM08-1B5PS-ZT1 | 1.5 mm | flush | PNP, normally open | M8 plug, 3 pins |
| Sick IME08-1B5PSZT0S | 1.5 mm / Sa 1.215 mm | flush | PNP, normally open | M8 plug, 3 pins |
| Sick IME08-02BPSZT0K | 2 mm / Sa 1.62 mm | flush | PNP, normally open | M8 plug, 3 pins |
| Sick IME08-02BPOZT0K | 2 mm / Sa 1.62 mm | flush | PNP, normally closed | M8 plug, 3 pins |
| Sick IME08-04NPSZT0K | 4 mm / Sa 3.24 mm | non-flush | PNP, normally open | M8 plug, 3 pins |
| Sick IMF08-02BPSNC0S | 2 mm / Sa 1.62 mm | flush | PNP, normally open | M12 plug, 4 pins |
| P+F NBB2-8GM30-E2 | 2 mm / sa 0…1.62 mm | flush | PNP, normally open, 5…30 V | cable 2 m |
| Omron E2A-S08KS02-M1-B1 | 2 mm ±10 % | shielded | PNP, normally open | M12 plug, 4 pins |
Two clarifications on this table. Despite the NC letters at the end of its code, IMF08-02BPSNC0S has a normally open output: that is what datasheet 1076745 states, and the normally closed sibling carries a different part number. Its housing is V4A stainless, IP68/IP69K, −40 to +100 °C, so it is a hygienic design. E2A-S08KS02-M1-B1 is stainless SUS 303 as well, and it is the only Omron item in our tables that we did not find on a discontinuation list. Caution is warranted: Omron withdrew much of the brass E2A line in 2022 (notice B-220184), our 2M variant is not on those lists, so we confirm the status of each E2A part number per enquiry.
M12
| Item | Sn / Sa | Installation | Output | Connection |
|---|---|---|---|---|
| Sick IME12-02BPSZC0S | 2 mm / Sa 1.62 mm | flush | PNP, normally open, 10…30 V | M12 plug, 4 pins |
| Sick IME12-04BPSZC0K | 4 mm / Sa 3.24 mm | flush | PNP, normally open | M12 plug, 4 pins |
| Sick IME12-04NPSZC0S | 4 mm / Sa 3.24 mm | non-flush | PNP, normally open | M12 plug, 4 pins |
| Sick IM12-04NPS-ZC1 | 4 mm | non-flush per the series code* | PNP | M12 plug |
| P+F NBB2-12GM50-E2-V1 | 2 mm / sa 0…1.62 mm | flush | PNP, normally open, 6…36 V | M12 plug, 3 pins |
| P+F NBB4-12GM50-E2-V1 | 4 mm / sa 0…3.24 mm | flush | PNP, normally open, 6…36 V | M12 plug, 3 pins |
| P+F NBN4-12GM50-E2 | 4 mm / sa 0…3.24 mm | non-flush | PNP, normally open, 6…36 V | cable 2 m |
| P+F NBN4-12GM50-E2-V1 | 4 mm / sa 0…3.24 mm | non-flush | PNP, normally open, 6…36 V | M12 plug, 3 pins** |
| P+F NJ2-12GM40-E2 | 2 mm / sa 0…1.62 mm | flush | PNP, normally open, 10…60 V, up to 3000 Hz | cable 2 m, stainless steel housing |
| P+F NJ4-12GM40-E2-5M | 4 mm / sa 0…3.24 mm | non-flush | PNP, normally open, 10…60 V | cable 5 m, stainless steel housing |
| SELET B60122POC5 | 2 mm | flush | PNP, normally open, 12…24 V | M12 connector (pins 1, 3 and 4 used; pin 2 free) |
| Omron E2A-M12KS04-WP-B2 | 4 mm ±10 % | shielded, standard body | PNP, normally closed | PVC cable 2 m |
* We could not find an official datasheet for this exact IM12-04NPS-ZC1 version: the link in our record points to a third-party shop. The letter N in that code position means non-flush on two verified siblings, IM18-08NPS-ZC1 and IME08-04NPSZT0K, so we treat it as unshielded on the strength of the series code. Before mounting it flush with metal, ask us: we will request the datasheet from Sick.
** The current NBN4-12GM50-E2-V1 datasheet (doc. 326161-0069) gives a 3-pin plug and a 6…36 V supply. The legacy documents for the same part number give 10…30 V, and 087768 also gives a 4-pin plug. See the block on the two revisions above.
A separate note on SELET. Its 12…24 V supply is narrower than the usual 10…30 V, and that is a real trap in a replacement: if your cabinet has a 12 V supply that sags, or logic at 10 V, the sensor falls outside its rated range. SELET also specifies hysteresis as a percentage of Sn rather than sr as Sick and P+F do, so its figures are not directly comparable with theirs.
M18
| Item | Sn / Sa | Installation | Output | Connection |
|---|---|---|---|---|
| P+F NBB5-18GM50-E2 | 5 mm / sa 0…4.05 mm | flush | PNP, normally open, 6…36 V† | cable 2 m |
| P+F NBB5-18GM50-E2-V1 | 5 mm / sa 0…4.05 mm | flush | PNP, normally open, 6…36 V | M12 plug, 3 pins |
| P+F NBB8-18GM50-E2-V1 | 8 mm / sa 0…6.48 mm | flush, datasheet 085501 (2020) lists "Increased operating distance" | PNP, normally open, 6…36 V† | M12 plug, 3 pins |
| P+F NBN8-18GM50-E2-V1 | 8 mm / sa 0…6.48 mm | non-flush | PNP, normally open, 6…36 V, −40 to +85 °C† | M12 plug, 3 pins (4 pins on the 2020 revision) |
| P+F NBB5-18GM40-Z0-V1 | 5 mm / sa 0…4.05 mm (0…3.8 mm in the cold) | flush | two-wire DC, normally open, 5…60 V, Im 2 mA | M12 plug, 3 pins |
| Sick IM18-08NPS-ZC1 | 8 mm | non-flush | PNP, normally open, 600 Hz | M12 plug, 4 pins |
| Balluff BES M18MI-PSC80B-BV03 (BES008F) | 8 mm / Sa 6.4 mm | flush (a datasheet footnote points to the mounting guide for long sensing distances, doc. 825357) | PNP, normally open, 10…30 V, IP68 | PVC cable 3 m |
| Omron E2A-M18LS08-M1-B3 | 8 mm ±10 % | shielded, long body | four-wire PNP, both outputs at once (NO and NC) | M12 plug, 4 pins |
† These rows come from the current datasheets. On the 2020 revisions the same part numbers give different numbers: NBB5-18GM50-E2 a 10…30 V supply instead of 6…36 V, NBB8-18GM50-E2-V1 500 Hz and 4 pins instead of 1350 Hz and 3, NBN8-18GM50-E2-V1 500 Hz and 4 pins instead of 1650 Hz and 3. The detail is above, under "One P+F part number can come with two datasheet revisions". We confirm the revision of the batch before shipping.
Note the last row. Omron's B3 suffix means a four-wire complementary scheme: normally open and normally closed signals are present on two separate outputs at the same time. Three consequences for a replacement: an existing three-core cable will not carry both outputs, the B3 body is 4 mm longer than B1 and B2, and the power-on readiness differs, 160 ms against 100. So B3 is chosen deliberately, for a circuit where one sensor is needed in the motion logic and the safety chain at once.
M30, block and flanged housings
| Item | Sn / Sa | Installation | Output | Connection |
|---|---|---|---|---|
| P+F NBB10-30GM50-E2-V1 | 10 mm / sa 0…8.1 mm | flush, M30×1.5 thread | PNP, normally open, 6…36 V, 1100 Hz | M12 plug, 3 pins |
| Omron E2A-M30KS15-WP-B2 | 15 mm ±10 % | shielded, standard body | PNP, normally closed, 250 Hz | PVC cable 2 m |
| P+F NBB15-U1-E2 | 15 mm / sa 0…12.15 mm | flush, flanged U1 body | PNP, normally open, 10…30 V, IP68/IP69K | terminal compartment, 0.5…2.5 mm² |
| P+F NBB15-U1-A2 | 15 mm / sa 0…12.15 mm | flush, flanged U1 body | four-wire PNP, both outputs at once, 10…30 V | terminal compartment |
| P+F NBB20-U1-UU | 20 mm / sa 0…16.2 mm, sr 18…22 mm | flush, flanged U1 body | two-wire AC/DC, Ue 24…250 V DC or 24…230 V AC, NO or NC logic set by wiring | terminal compartment + external 3 A / 300 V fuse to UL 248 |
| P+F NBB20-L2-E2-V1 | 20 mm / sa 0…16.2 mm | flush, L2 block | PNP, normally open, 10…30 V, 440 Hz | M12 plug, 4 pins |
| P+F NBB20-L2-A2-V1 | 20 mm / sa 0…16.2 mm | flush, L2 block | four-wire PNP, both outputs at once, 10…30 V | M12 plug, 4 pins |
| P+F NBN40-L2-A2-V1 | 40 mm / sa 0…32.4 mm, sr 36…44 mm | non-flush, L2 block | four-wire PNP, both outputs at once, 10…30 V | M12 plug, 4 pins |
| Sick IQ40-40NPPKC0K | 40 mm / Sa 32.4 mm | non-flush, 40×40×66 mm block | four-wire PNP, complementary, 10…30 V, IP67/IP68/IP69K | M12 plug, 4 pins, push-lock mount supplied |
The IQ40 datasheet names this output in a row reading Output function: Complementary. Pepperl+Fuchs calls the same arrangement antivalent in its documents, suffixes A0 and A2, so in the tables above the two words mean the same thing.
A separate word on the U1 and L2 bodies, because people often buy them "instead of an M30". They are not barrels for a nut. U1 mounts through the flange on its base: four holes in a rectangle, 60 mm between centres along the length and 30 mm across, tightening torque 1.8 Nm. The M20×1.5 thread visible on the drawing is the cable entry, not a place to screw it into a boss. Wiring on U1 goes through a terminal compartment for 0.5…2.5 mm² conductors, so you bring your own cable, no more than two conductors of equal cross section per terminal. L2 is a rectangular block for bolts. If the machine has an M30 in a boss, a U1 or L2 means reworking the bracket.
The IFM items
The catalogue holds 14 IFM inductive sensors. An honest caveat: the Sn, installation type and output type fields in our records for these items are not populated, and we could not open the official ifm datasheet for this article for technical reasons. So we are not printing figures here that we have not seen in the document: doing that would be precisely what this whole article argues against.
What we can state for certain. The short ifm article number (IGS206 or IGM204, for example) encodes no parameters: in the datasheet it is paired with a long order code of the form IGB3008BAPKG/US-104. That long code is the one to quote when you write to us. We will request the datasheet against it and return the five fields in the same form as the tables above. And if you need a working replacement rather than the same article number, we will select a Sick or Pepperl+Fuchs equivalent by the procedure above and show the five-field calculation.
Items: IF5712, IF6030, IFS214, IFT200, IFT202, IFT203, IGC220, IGC221, IGM204, IGS206, IGS232, II0097, II5916, IIS206. The full brand listing: IFM sensors in the catalogue.
What budget to expect
We are not printing specific figures: prices in this group are pegged to the exchange rate and recalculated, so a number baked into the article would go stale within a month. The orders of magnitude are these.
The cheapest entry is the cylindrical M8 and M12 parts in the Sick IME and Pepperl+Fuchs NBB and NBN series. The brands' price bands overlap here, so the cheaper item turns up in either one, and the spread inside a band is roughly twofold. More expensive are the versions with an extra property: a stainless housing (P+F NJ, SELET), a hygienic design (Sick IMF), a block or flanged body for a long range (Sick IQ40, P+F L2 and U1), a complementary A2 output, two-wire AC/DC. The two most expensive items in this article are NBB20-U1-UU with its 250 V terminal compartment and the top IFM item, which costs more than ten times the cheapest Sick IME. The full brand listings: Sick sensors and Pepperl+Fuchs sensors.
The current price always sits on the item's own page and is recalculated with the exchange rate, so read it there rather than in an article. Lead time we confirm per enquiry for each part number: some part numbers are available for supply, others are discontinued or built to order.
The practical takeaway. If you are replacing an ordinary three-wire sensor in a dry workshop, stay with the cylindrical Sick IME and P+F NBB and NBN series: they cover flush and non-flush, and 2, 4, 5, 8 and 10 mm. Pay more only for a specific property: a stainless housing for washdown, a complementary output for a safety chain, AC/DC for switching a coil directly, a block housing for a long range. Tell us the job and we will show you which item solves it for less.
If the original brand is no longer supplied
The procedure is the same; the input data just has to come off the equipment rather than out of a catalogue. We walk these six steps with the customer when they send photos of the installation.
- Measure the housing thread and length with calipers. That gives you the first field.
- Look at how the sensor sits. A face flush with metal means shielded is required. Face protruding with free space around it? Then unshielded will do.
- Measure the actual gap to the target at the mechanism's extreme position. That is your requirement on Sa, not on Sn.
- Establish the target material. Steel, stainless and aluminium are three different answers.
- Establish the output type. If the marking has worn off, measure it with a multimeter: apply power, measure the voltage between the output and the negative rail, bring metal close. Positive appearing at the output means PNP; a pull-down to negative means NPN. The full procedure with the common mistakes is in how to test a proximity sensor with a multimeter.
- Compute the Sn you need: divide the actual gap by 0.81, by the material factor and by the 0.8 margin, then round up to an available rating.
The same calculation run backwards. Gap 3 mm, target in stainless steel 304, M18 housing flush with a plate. Shielded is required. The stainless factor on shielded M18 parts from Pepperl+Fuchs is 0.73 or 0.74 depending on the model. Required range: 3 ÷ 0.8 ÷ 0.81 ÷ 0.74 = 6.26 mm. The 5 mm option fails; the nearest workable rating in the catalogue is 8 mm. Running this before ordering is worth it, because reworking a bracket for a different housing diameter costs more than the price difference between a 5 mm and an 8 mm sensor.
One separate and frequent case: the brass Omron E2A line. The manufacturer discontinued much of it in 2022 with E2E-Next as the recommended replacement, and that is exactly why "what replaces an E2A" reaches us regularly. The stainless E2A-S remains current. Two implications for you. Re-ordering a discontinued item from the manufacturer may be impossible, so we confirm availability and lead time on E2A separately per enquiry. And if you have a brass E2A in service, it makes sense to compute a replacement on Sick IME or P+F NBB using the procedure above rather than keep hunting for the same part number.
Four traps that derail a replacement
- Sizing on Sn without the multipliers. A 3 mm gap and a "4 mm" sensor look compatible until you account for 0.81, the material factor and a margin for vibration.
- Shielded replaced with unshielded. The sensor latches on in the metal boss, and it looks like a factory defect.
- Output type not checked. The sensor is alive, the signal line sees nothing. A day goes into chasing a fault that does not exist. A sub-case: a four-wire complementary sensor in a three-core cable.
- Two-wire fitted in place of three-wire. The PLC input latches on residual current, or the sensor never switches because the load draws less than the minimum operating current.
Frequently asked questions
What is Sa and why is it not in the catalogue?
It is the assured operating distance: the distance at which the sensor must switch across its whole voltage and temperature range. IEC 60947-5-2 defines it as a range from zero to 0.81 of rated Sn. Manufacturers write it down differently: Pepperl+Fuchs prints the fork, "sa 0…4.05 mm", while Sick and Balluff print only the upper bound as a single figure, "Safe sensing range Sa 1.62 mm" or "Sa 6.4 mm". The zero lower bound comes from the standard, not from the datasheet. Mountings are designed against Sa, while the catalogue Sn serves to compare models with each other. Omron does not print Sa at all: the E2A datasheet carries a Setting distance row in millimetres, for example "0 to 6.4 mm" at Sn 8 mm. The 0.8 ratio holds in every column, but the formula 0.8·Sn itself is not in the datasheet.
Why is Sn called a conventional quantity?
Because the standard itself calls it that. Clause 2.3.1.1 states that the rated operating distance takes into account neither manufacturing tolerances nor the influence of voltage and temperature. What is measured is the effective distance sr, and there is only one requirement on it: to fall within ±10 % of Sn at rated voltage and 23 °C. So two sensors both rated Sn 8 mm may measure 7.2 and 8.8 mm, and both are within spec.
How large must the target be for the datasheet range to hold?
The standard defines the target as a square of Fe 360 steel, 1 mm thick. The side length equals the diameter of the circle inscribed on the active surface of the sensing face, or three times Sn, whichever is greater. For a sensor rated Sn 8 mm that is 24 mm. If your target is smaller or thinner, the range drops, and the datasheet figure has to be reduced for that as well.
Can I fit a larger-diameter sensor if the required range will not fit?
Yes, and it is the standard answer. Going from M12 to M18 gives a longer Sn at the same installation type. Check only two things: whether there is room in the bracket, and whether the new housing intrudes into the mechanism's path. Moving to an L2 block or a flanged U1 gives a longer range still, but that is a mounting rework, because they do not screw into a boss.
Are same-size sensors from different brands interchangeable?
Mechanically, usually yes: an M12 or M18 thread is standard. Electrically and on range, no. Beyond the five fields, check the supply range too: SELET series B60 is 12…24 V, Sick IME is 10…30 V, P+F NBB and NBN are 6…36 V, NJ is 10…60 V. Housing length and the cable exit point differ as well, so measure the protrusion in the bracket. Some concrete figures: NBB5-18GM50-E2 is 56 mm long, its plug version 66 mm, Balluff BES008F 55 mm, and the Omron E2A-M18LS08 in its B3 version is another 4 mm longer than B1.
Why do material factor tables differ between sources?
Because the factor is a property of the specific model, not a physical constant. It depends on the housing material and the shielding design. At Sick the IME series gives around 0.45 for aluminium, the hygienic IMF 0.43, the block-shaped IQ40 0.34. At Pepperl+Fuchs the range across models runs from 0.23 on NJ2 to 0.50 on NBB10. The single part number NBB5-18GM50-E2 shows 0.35 and 0.30 across two datasheet revisions. Take the value from the datasheet of the model you are buying; if you have no datasheet to hand, send us the part number and we will send you the row from the document.
Can a sensor that looks identical have the opposite output logic?
It can, and that is a reason in itself to check the suffix. On Omron E2A the B1 suffix means a normally open output and B2 means normally closed. Two sensors of the same diameter with the same range and the same PNP output will work in opposite logic. Of our items, E2A-S08KS02-M1-B1 is normally open, while E2A-M12KS04-WP-B2 and E2A-M30KS15-WP-B2 are normally closed. Sick encodes the same thing in one letter: IME08-02BPSZT0K is normally open, IME08-02BPOZT0K is normally closed, and it is the only NC Sick item in our tables.
How far apart can two sensors be mounted?
Manufacturers give this on a separate drawing, and the figures depend on the model rather than on a "few diameters" rule. The Sick IME12-04NPSZC0S datasheet (unshielded, M12, Sn 4 mm) prints six dimensions in its non-flush installation block: A 12, B 24, C 12, D 12, E 8, F 32 mm. So two adjacent M12 sensors need 24 mm between centres, and two facing each other need 32 mm. For the shielded IME12-04BPSZC0K the flush block keeps B 24, C 12, D 12 and F 32 mm. For the hygienic IMF08 on M8 the figures are smaller: B 6.5, C 8, D 6, F 16 mm. And for the block-shaped IQ40 at Sn 40 mm they rise sharply: A 42, B 150, C 40, D 120, E 40, F 150 mm. The letters A to F in Sick datasheets are marked on the drawing only, with no text legend, so check against the drawing itself rather than against the letters in this paragraph. If you have no datasheet to hand, send us the part number and we will send the page with the dimensions.
The sensor is shielded and still triggers off the machine frame
Check the side clearance and whether a second sensor sits nearby. Shielded parts also have limits on adjacent metal, just softer ones than unshielded parts: see the figures in the previous question. The second cause we see regularly: an identical sensor mounted closer than the datasheet distance, so the oscillators start influencing each other and both channels switch erratically for no visible reason.
Are there sensors with the same range on every metal?
That class exists; manufacturers label it all-metal or factor 1. There are no such items in our catalogue at the moment, and we are not going to invent them. Two workable routes. First: compensate the factor with a longer Sn using the formula above. For aluminium that is usually one size up, and it is almost always cheaper than factor 1. Second: if the gap leaves no room to compensate, send us the thread, the gap and the material through contacts. We will price a factor-1 item to order and give you the lead time before you commit.
What to do next
If all five fields are known, pick from the tables above. If any field is in doubt, send us five things: the housing thread, the actual gap, the target material, the controller input type, and photos of the installation. We will check against the manufacturer's datasheet, send back the calculation using the formula from this article, and propose an item from the catalogue. Write or call us, and if nothing fits your job we will say so directly rather than sell you a "similar" sensor.
The items in these tables are published in the catalogue. Availability and lead time are confirmed per enquiry: the manufacturer discontinued much of the brass Omron E2A line in 2022, so for those parts we check the status against each individual part number. Exchange and return terms are set out in writing together with the invoice, because the periods differ for a private individual and for a company; your sales manager will give the exact figure for your buyer type before payment.
Catalogue: Sick sensors, Pepperl+Fuchs sensors, Omron sensors, IFM sensors, and the full base at all industrial sensors.
Related reading: how an inductive sensor works and how to select one, testing a sensor with a multimeter, connecting a sensor to a PLC, comparing proximity sensor types. If the target is non-metallic, an inductive sensor will not work at all: see optical sensors.
