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Operation and Wiring
Standard Wiring
The Model 640/641/645/646 B Series operates from a standard 2-Wire, 4-20mA loop. If using a loop powered
unit, attach the positive (+) input from the power supply to Pin A or
Red
wire on the sensor and the negative (-)
input from the power supply to Pin B or
Blue
Wire of the sensor.
Figure 1
– wiring: loop powered
Figure 2
– wiring: loop powered/DC source
If using a standard DC power supply, install either an ammeter and/or load resistor in line with the output, Pin B or
Blue
Wire.
The resistor will generate a DC voltage that is proportional to current by:
V = IR
If R = 500 ohms and I = 6 mA, then V = 3 VDC
Note:
- Resistor value must be less than: (Vsupply
– 12) x 50.
- For integral cable sensors: RED wire is positive, BLUE wire is negative.
