VH-4DO-TN Veichi VH-4DO-TN Expansion module: Transistor (NPN), compatible with the VH series.

VH-4DO-TN — a left-side digital output board for the VH-series PLC: 4 transistor outputs, NPN type. It plugs into the left of a VH300/VH500/VH600 CPU; one left board per host. You pick it when the CPU is short exactly a few outputs for relay coils, solenoids or indicator lamps.

Typical applications:

• Driving interposing relays, pneumatic valves, solenoids.
• Indicator lamps, status signaling.
• Fast switching of DC loads where a relay is too slow.

Worth noting: the outputs are transistor NPN — DC switching, not AC; for AC loads add an interposing relay. If you need inputs instead of outputs, choose VH-4DI. The clock version is VH-4DO-TN-RTC.

Veichi VH-L — left-side expansion boards for the VH PLC series

VH-L is a family of left-side expansion boards for the modular Veichi VH300/VH500/VH600 PLCs. These are not controllers — they do not work on their own; they plug into the left of the CPU as a small add-on board. The key rule: only one left board fits per CPU. So here you choose not «how many» but «which one» — to match the signal you need.

The left slot is handy because it adds a few channels right on the PLC body without using up your right-side module count. VH-L offers boards for analog (current or voltage), digital inputs and outputs, RS485 and a dedicated real-time clock (RTC) board. Almost every board comes in a plain and an RTC version.

How the VH-L boards are grouped

• Analog current: VH-2AD1DA-I — 2 current inputs + 1 current output (4–20 mA).
• Analog voltage: VH-2AD1DA-V — 2 inputs + 1 output by voltage (0–10 V).
• Digital in/out: VH-4DI — 4 inputs; VH-4DO-TN — 4 transistor NPN outputs.
• Communication: VH-RS485 — two extra RS485 ports for Modbus.
• Clock: VH-RTC — a standalone RTC board; other boards have an RTC version with the -RTC suffix.

How VH-L differs from the right-side VH-R modules

In practice the left board covers the «last» few channels or the clock, while the main I/O expansion is done with the right-side VH-R modules. If a single left slot is not enough, the right modules take over.

When VH-L is not the right pick

• You need many I/O channels — there is only one left slot, so use the right-side VH-R modules.
• The host is not a VH-series PLC (e.g. VC1/VC3/VC5) — those use their own VC modules; see the Veichi PLC catalog.
• You need the CPU itself, not an expansion board — that is the VH300/VH500/VH600.
• You are building on another brand — compare with Delta or Fatek.

Our experience with VH-L

Left-side boards are bought for specific gaps: when a VH CPU is short exactly one or two analog channels, a pair of RS485 ports, or needs a clock for logs and schedules. The typical buyer question is «current or voltage»: for 4–20 mA sensors it is the -I version, for 0–10 V signals the -V version. People often add Veichi VFDs and operator panels for the same machine.