Terminals of the Frequency Converter
In addition to the main power inputs and outputs for connecting the frequency converter to the power supply and electric motor, there are a number of additional terminals for connecting various devices. In this article, we will discuss the main types of these inputs and outputs, as well as their features.
Discrete Inputs
Discrete inputs can be in one of two states: signal present or signal absent, that is, "on" or "off." Typically, various buttons and switches are connected to such inputs, and less frequently – sensors or outputs of control relays. For example, several switches can be connected to discrete inputs, and each output can be programmed to one of the operating frequencies of the converter. This is convenient as the buttons can be located at a significant distance from the device.
It is also possible to assign a reverse function to one of the switches. If a discrete input receives a signal from an external relay, it allows the converter to be automatically started depending on the status of a specific technological unit.
Analog Inputs
Most frequency converters have a standard set of analog outputs: 0-10 V and 4-20 mA. These outputs are typically intended for connecting cables from various sensors or other devices. Some outputs may be combined, allowing the operating mode to be set by installing the appropriate jumpers.
One standard way to use a 0-10V type input is to connect an external variable resistor (from one to several tens of kilo-ohms). By changing the resistance, one can adjust the frequency of the output voltage and the speed of the motor. 4-20 mA type outputs are usually used for connecting to various sensors, such as pressure sensors, temperature sensors, and others. These inputs are characterized by high signal accuracy and increased noise immunity.
Discrete Outputs
These contacts can also be in one of two states: "on" or "off." It is important to understand the difference between the two types of discrete outputs: outputs with dry contacts and outputs with open collectors. Dry contacts can be used for switching signals from various devices.
Discrete outputs can be configured to control a group of pumps using one common converter or used for transmitting emergency signals for alerts, such as sirens and alarms. When connecting external devices to these outputs, it is necessary to pay attention to the compatibility of the switched currents and voltages.
Digital Interfaces
Many modern frequency converters have one or more digital interfaces for exchanging information with external devices, such as computers or control panels. This is typically implemented according to RS485, CAN, USB standards, or other, less common ones. Control signals from various software protocols can be transmitted over the same interface. It is recommended to clarify whether the converter supports the chosen exchange standard at the time of purchase.
Some models of frequency converters may also have special input-output ports. Information about their purpose and usage features can be found in the manual or by contacting the manufacturer's support service.