Connect 4-20mA Sensor to mV-485 Adapter
- Wiring the sensor. A 56 Ohm resistor is required to convert mA to mV.
- Configure the mv-485 Adapter. Connect using iChart (Connecting to a mV-485 Adapter)
- Set 4-20mA scaling. Under “Edit Sensor”, select “Generic” from the drop down list. Use 224 mV and 1120 mV for scaling:
Point 1: mV1 = 224; Value1 = <value corresponds to 4 mA>
Point 2: mV2 = 1120; Value2 = <value corresponds to 20 mA>
The screenshot below shows an example of a 4-20 mA temperature sensor with 4mA = 0C and 20mA = 50C.
- Test the connection. Most 4-20 mA transmitter has a test function where the output is lock to 4mA and 20mA or set to arbitrary mA value for testing.
- Lock the sensor output to 4 mA, read mV (Reg: 0x0002). It should read around 224 mV
- Lock the sensor output to 20 mA, read mV (Reg: 0x0002), it should read around 1220 mV
- Set the sensor output to an arbitrary mA output, read mV, divide the mV by 56 to convert to mA. Verify this is what the sensor output is set to.
Converting mV to sensor reading
mV is from the “Read mV” function from step 4
mV1, Value1 are Point 1 scale from step 3
mV2, Value2 are Point 2 scale from step 3
Use the temperature sensor example in step 3. If the mV reading is 672 mV,