How Do I Connect the 4-20mA Signal from My Transmitter to Third-Party Equipment?
The TD100 T22 transmitter provides a 4-20 mA output signal that can be used to send liquid level data to a third-party device, such as a control system or display system. This article covers how to wire the TD100 T22 transmitter to your third-party equipment.
Note: These instructions only cover the wiring between a single TD100 T22 transmitter, the FINCH display, and the third-party device receiving the 4-20 mA output signal. For other wiring information for your system, see Installing a New System.
Procedure
Wiring Instructions for a Non-Isolated Setup
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Power, Ground, and SV Signal Connections
- Connect the PWR pin on the TD Transmitter to the PWR pin on the COMP#1 / TD80#1 terminal block of the FINCH II Board using the black wire.
- Connect the GND pin on the TD Transmitter to the GND pin on the COMP#1 / TD80#1 terminal block of the FINCH II Board using the white wire.
- Connect the SVBUS pin on the TD Transmitter to the SV pin on the COMP#1 / TD80#1 terminal block of the FINCH II Board using the red wire.
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4-20mA Output to Third-Party Device
- Connect the LOOP + pin on the TD Transmitter directly to the PWR pin on the TD Transmitter.
- Connect the LOOP - pin on the TD Transmitter directly to the positive input of the third-party device.
- Connect the negative input of the third-party device to GND.
- Refer to the third-party device's product manual for the required input voltage, and whether additional components (such as resistors) are needed to wire the 4-20 mA signal to the device.
! Important Note: Input Voltage Requirements
The Titan current loop requires specific power conditions to correctly interface with the third-party device:
- The voltage supplied to the Loop + pin (pin 4) on the TD100 T22 should be at least 50% greater than the working voltage of the loop receiver input on the third-party device.
- Example: if the third-party device accepts a 0-5V input, you need at least 7.5V supplied to pin 4 (12V is commonly used). For a 0-10V input, the voltage supplied to the Loop + pin should be at least 15V, which may require an external power supply.
- Determining receiver input requirements:
- Check device specifications: confirm the receiver's input voltage range (e.g., 0-5V or 0-10V).
- Measure sensing resistor value: measure resistance between the 4-20mA input contact and ground:
- 250 ohms indicates a 0-5V input.
- 500 ohms indicates a 0-10V input.
If the supplied voltage is too low, the 4-20mA signal may not work as expected.