How do I connect the 4-20mA signal from my transmitter to third party equipment?

Overview:

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 include the wiring for a single TD100 T22 transmitter to the FINCH display and the third-party device that the 4-20 mA output signal is being sent to. For other information relating to the wiring of your system, please refer to the installation knowledge base articles here.

Wiring Instructions for a Non-Isolated Setup:

1. 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.
2. 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 product manual for the required input voltage and if any additional components, such as resistors, are needed to wire the 4-20 mA signal wires 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 (pin 4) 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.