3.4
Current Output Units – 9 pin D-sub Connector electrical Termination
The Model 267 and 267MR is a two wire loop-powered 4 to 20 mA current output unit (see Diagram
6). The current flows into +EXC. Pin4 (+EXC.) and returns back to the power supply through
Pin 9 (-EXC) (see Diagram 7). The power supply must be a DC voltage source with a voltage range
between 9 and 30 measured between Pin 4 and Pin 9 (-EXC.). The unit is calibrated with a 24 VDC
loop supply voltage and a 250ohm load. The current output 9 pin D-sub connector pin designations are
shown in Diagram 8.
CONNECTION
9 pin D-sub Connector
Electrical Termination
+EXCITATION
4
+OUTPUT
9
Diagram 7
Diagram 8
3.5 4-20 mA Circuit Diagram
Minimum Supply Voltage (VDC) = 9 + 0.02 x (resistance of receiver plus line)
Maximum Supply Voltage (VDC) = 30 + 0.004 x (resistance of receiver plus line)
If the current loop has a current limiter, threshold should be adjusted to 35 mA minimum
(see Diagram 9).
Loop Power Supply
vs.
Loop Resistance for 4 to 20 mA Current Tranducers
Diagram 9
Operating
Range
30
9
800
0
Loop Resistance (Ohms)
Loop Supply Voltage (VDC)
PIN 4
PIN 9
- EXC
PIN 1
PIN 4
PIN 1
