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This homemade calibrator will produce 4-30mA, which can be used in place of various sensors giving signal as 4-20mA in its wide range of input. To keep it simple, this will simulate 4-20mA or called as 4-20mA Signal Generator.

Examples:

Danfoss Pressure Transmitter MBS3050

Danfoss Temperature Tranmitter MBT3560

Emerson Level Sensor Rosemount 3101

It is useful for Shipboard and Industrial sensors.

Step 1: Parts Required

LM317 Voltage, Current Regulator

39 Ohms Resistor

Berg Strips

250 Ohms Variable Resistor

4 x Banana Jacks Female

Heatsink

Enclosure

MiniUSB Female connector

9V Battery Connector

2 x Leds and 1K Ohms Resistors

Some Screws

Dupont wires

Veroboard

Step 2: Testing

Using ElectroDroid Android App, have calculated the required resistance of 39 Ohms for 32mA taking 2mA as losses and 39Ohms is readily available in the market.

Testing the circuit in Breadboard giving desired output. Upto 30mA.

Step 3: Schematic

Self Explanatory

Step 4: Prototyping and Soldering

Design the circuit to suit into the enclosure. Since only few components are required fairly moderate size enclosure can accommodate giving enough space for soldering.

Step 5: Finishing

  • Use Bergstrips for connection from upper part of enclosure to lower part. To easily seperate for access.
  • Leave a enough size hole to access Potentiometer.
  • 1 Pair of Banana jacks for Output and other pair is for connection to Multimeter. For testing connect two red jacks as shown in video.
  • Input can vary from 5V to 24V through Miniusb. 9V 6F22 Battery can also be used for portability.
  • LM317 is operating as a current regulator.
  • Green led here is a power on led and Blue led is just to illuminate the enclosure from inside as I don't have any white led's lying around.
  • Crimp the duponts and ring connectors for firm connection to the banana jacks.

- Kumaran

kua201@gmail.com

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