How To Measure 4-20mA Temperature Sensor

OT26 4-20mA Submersible Temperature Introduction

OST26 Is a 4-20mA temperature sensor that is fully submersible in 

• Water
• Rain Water
• Chemical Tanks ( check compatibility)
• Fluid
• Marine Water

The output of this temperature sensor is 4-20mA , 4-20mA the industry standard output type for long runs of cable 3m to 100m

The 4-20mA Temperature Sensor range

The output 4-20mA is scaled to the temperature range of the sensor.

Output examples

OST26 has customisable temperature range that can be changed dynamically. there are the popular output types and there respective scaling

4-20mA -10℃ to 60℃ Output Table

4-20mA 0℃ to 50℃ Output Table

4-20mA 0℃ to 100℃ Output Table

4-20mA 0℃ to 35℃ Output table

Meter set up

To Measure the 4-20mA output Temperature sensor 2 parameters need to be met

• Power source - Power needs to be applied to the sensor
• Current meter - Measure the current the sensor draws

The current meter needs to be placed in series to the -Ve connection the Ground or 0V

Measure with The following steps

• Apply Positive Voltage to the red wire
• Take 2 probes from the Current Meter
  • First +Ve Probe from the current meter on -Ve wire
  • Second Probe from the current meter to GND or 0V

4-20mA Temperature Sensor measurement diagram

The current meter will display the current draw of the sensor . The current draw will correspond to temperature

• 0% of Temperature Scale = 4mA
• 50% of Temperature Scale = 12mA
• 100% of Temperature Scale = 20mA

Convert 4-20mA to Volts

4-20mA is an excellent topology to measure when long cable runs are required, Voltage output is not used because the long cable run will incur a Voltage drop affecting the measurement reading.

At the termination point It is common to convert the 4-20mA to a voltage using Ohms law

A shunt Resistor will convert the 4-20mA to a Voltage. The shunt resistor is placed in the position indicated in the diagram below

common values are outlined below. 

Ohms law 

• V (Voltage) = I (Current) * R(Resistance)
• I(Current) = V(Voltage)/R(Resistance)
• R(Resistance = V(Voltage)/R(Resistance)

4-20mA to 1-5V

1V/4mA=250R

4-20mA to 2-10V

2V/4mA=250R