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Configuring 4-20mA sensor readings on the Hawk

Written by Matthew Clark-Massera

Updated at March 12th, 2025

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Table of Contents

Wiring Configuration Configure Task Example: Configure Ag-Tech1 parameters 3V3 Sensor 5V or 12V Sensor 4-20mA parameters Reading Conversion Reading Resolution and Accuracy

The 4-20mA interface is common for industrial sensors. Such sensors output an amperage between 4mA and 20mA proportional to the signal (pressure, temperature, moisture, vibration) they are measuring. 

Wiring

The wiring of 4-20mA sensors differs depending on the specific sensor, and depending on the specific card you are using.

Agtech1, RS1 and Bluetooth+ Card

To properly use a 4-20mA sensor with the Hawk, you need to wire it sensor into:

  1. A 4-20mA input on the Hawk card.
  2. The Vboost or 3v3 Switch Power on the Hawk Card
  3. GND (on the baseboard)

For details on different cards IOs, please see this article.

When using the Ag-Tech1 plug-in card, the I/Os of interest are:

Function Agtech1 IO RS-1 IO

Bluetooth+ IO

VBoost 2 2

8

3.3V output 5 5

7

4-20mA 9 9

1

4-20mA sensors typically come with 3 wires, and the below connections should be made:

4-20mA Sensor Line Connection
VCC
(Voltage Input - usually 3V3 or 5V)
  • 3V3 sensor: connect to  3V3 output
  • 5V Sensor: Connect to  VBoost
GND Connect to Hawk GND
4-20mA Signal Line Connect to  4-20mA input

For 2 wire connections, the 4-20mA Signal line acts as the GND.

For 2 wire configurations, the VCC cable should be wired into 3v3 or Vboost, and the 4-20mA signal line into the 4-20mA input.

 
 

4-20mA Card

4-20mA sensors typically come with 3 wires, and for the 4-20mA Card, the below connections should be made:

4-20mA Sensor Line Connection
VCC
(Voltage Input - usually 3V3 or 5V)
  • 3V3 sensor: connect to  3V3 output
  • 5V Sensor: Connect to  VBoost
4-20mA - (GND) Connect to 4-20mA -
4-20mA + (Signal line) Connect to  4-20mA +
 
 

 

Configuration

We now need to configure the Hawk to

  1. Wake up on a schedule to take a reading - (Set up a Task)
  2. Power on the sensor at the correct voltage (via the Vboost or 3V3 rail)
  3. Sample the sensor after some time (warm up delay)
  4. Log the reading and optionally upload. 

Configure Task

Configure a task at your chosen frequency - choosing 4-20mA Action 1 as an action.

Example: Configure Ag-Tech1 parameters

3V3 Sensor

If we have a 3V3 Sensor, we configure the 3V3 rail to be powered when the 4-20mA Action is done.

5V or 12V Sensor

If we have a 5V/12V sensor, we set the Vboost rail to be activated when doing a 4-20mA action.

We can set the Vboost Output Voltage Level to 5V or 12V

4-20mA parameters

Set the power on delay and the Analogue which the reading should be mapped to.

Reading Conversion

The reading is reported in µA - divide by 1000 to get to mA

i.e. a reading of 4250 seen in the data = 4.250mA

Reading Resolution and Accuracy

4-20mA Card

12 bit resolution.

Full scale is 0-22mA.

Each step size is ~5.37 μA

Readings are typically ~2% accurate

 
 

Other Cards

12 bit resolution.

Full scale is 0-33mA.

Each step size is ~8.06 μA

Readings are typically ~2% accurate

 
 

 

4-20ma sensor config configuration hawk

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