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 (see Connecting to a mV-485 Adapter).
- Set 4-20mA scaling. In the Edit Sensor field of the Configuration menu, select Generic from the drop down list. Use 224 mV and 1120 mV for scaling:
Point 1: mV1 = 224; Value1 = <value corresponding to 4 mA>
Point 2: mV2 = 1120; Value2 = <value corresponding 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 transmitters have a test function where the output is locked to 4mA and 20mA or set to an 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.
- Convert mV to sensor reading. Use the following equation to convert from mV to measurement units:
- 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:
Connecting mV-RS485 adapter to NexSens UW-FWP
The receptacle end of the mV-RS485 adapter may be connected to the plug end of the NexSens UW-Field Wireable Plug (UW-FWP). Below are the pinouts of the mV-RS485 adapter and UW-FWP, along with the signals that are passed through to the J terminals on the UW-FWP.
Note: For 4-20 mA sensors, a 56-ohm resistor must be jumped between mV+ and mV-.
|mV-RS485 receptacle pin number||UW-FWP plug pin number||UW-FWP||Actual Signal|
*In some applications (i.e., using a loop powered 4-20 mA sensor), a common ground must be established between all ground sources including mV- and ground on the UW-FWP.