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How to Connect a 4-20mA Current Loop Pressure Transmitter

4-20mA Current Loop Pressure TransmitterAll devices connected to make up a 4 to 20 milliamp current loop are connected in series.

The devices that are typically connected together include:

  1. Pressure Transmitter
  2. Input Device to accept the signal from the Pressure Transmitter such as a Programmable Logic Controller (PLC), Controller, Panel Meter, Analog to Digital Converter (ADC) or Signal Conditioning Unit (SCU)
  3. Sensor Power Supply to power the Pressure Transmitter such as a Programmable Power Supply unit, DC Power Supply Unit (PSU), AC/DC Voltage Regulated Transformer or a DC Battery

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A) If the 4-20mA Input Device includes an Internal Sensor Power Supply and has 2 input connections:

  1. Connect Positive (+) Input connection to Positive (+) Pressure Transmitter connection
  2. Connect Negative (-) Input connection to Negative (-) Pressure Transmitter connection

B) If the 4-20mA Input Device requires an External Sensor Power Supply and has 2 input connections:

  1. Connect Positive (+) External Sensor Power Supply connection to Positive (+) Pressure Transmitter connection
  2. Connect Negative (-) Pressure Transmitter connection to Positive (+) Input connection
  3. Connect Negative (-) Input connection to Negative (-) External Sensor Power Supply connection

C) If the 4-20mA Input Device includes an Internal Sensor Power Supply and has 2 input connections plus 2 supply connections:

  1. Connect Positive (+) Internal Sensor Power Supply connection to Positive (+) Pressure Transmitter connection
  2. Connect Negative (-) Pressure Transmitter connection to Positive (+) Input connection
  3. Connect Negative (-) Input connection to Negative (-) Internal Sensor Power Supply connection

Some Input Devices bridge the Negative (-) Input connection to the Negative (-) Internal Sensor Power Supply via an internal / external jumper or link.

If the input device only includes a Voltage input, it can be easily adapted to measure a 4-20mA signal by adding a 250 Ohm load resistor across the Positive (+) and Negative (-) Input connections.  This will generate a voltage drop of between 1 and 5 Volts which is directly proportional to the 4-20mA signal.

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Related Help Guides

  • Transforming a 2 wire Current Loop into a Voltage Output Signal
  • How do you measure flow rate with a dp cell
  • Supply voltage and load resistance considerations for pressure transmitters
  • Advantages and Disadvantages of using a 4 to 20 mA Signal
  • What is difference between working, burst and over pressure
  • What can cause random variation in pressure transducer output
  • Why use 4-20mA and 3-15 psi rather than 0-20mA & 0-15psi
  • How to get a 10 volt signal from a 4-20mA output pressure sensor
  • What is the difference between a pressure transducer and a transmitter
  • Does the type of Engineering Units matter for Pressure Transmitters
  • Choosing calibrator for pressure transmitters
  • How to create a list of specification parameters for a pressure sensor

Related Technical Terms

  • 2 Wire
  • 4 to 20 mA Current Loop Output Signal
  • HART®
  • Isolation Diaphragm
  • Square Root Extraction
  • Stainless Steel Pressure Sensors
  • Transmitter
  • Turndown Ratio

Related Online Tools

  • Pressure Transmitter 4-20mA Current Output Calculator
  • Flow Transmitter 4-20mA Current Output Calculator
  • DP Flow Transmitter Output Calculator
  • 4-20mA Signal to Measurement Reading Converter
  • SqRt Extraction 4-20mA Signal to Measurement Reading Converter
  • Temperature Transmitter 4-20mA Current Output Calculator
  • Liquid Level Transmitter 4-20mA Current Output Calculator
  • 4 to 20 mA Supply, Load, Shunt and Signal Calculator
  • Pressure Transmitter 0-20mA Current Output Calculator

Related Product and Application Guides

  • Pressure Transmitters

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Wirelessly Measure & Log 4-20mA

Use this battery powered wireless 4-20mA wireless transmitter to transmit readings to a receiver connected to USB, RS485, RS232, cellular network or analog output

Use this battery powered 4-20mA wireless transmitter to transmit readings to a receiver connected to USB, RS485, RS232, cellular network or analog output

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