PART TWO - INSTALLATION
SECTION 3 - ELECTRICAL CONNECTIONS
Model 692P
Rev. 9-898
-16-
drop across the transmitter is at least 16 VDC, but
not more than 40 VDC.
B. The load(s) in the circuit will generally have some
electrical resistance, 100 ohms for example. The 4-
20 mA loop current will produce a voltage drop
across each load. The maximum voltage drop will
exist when the loop current is 20 mA. The power
supply must provide enough voltage for this drop
plus the 16 VDC minimum required for the Model
692. Two examples illustrate this point:
EXAMPLE 1
Sufficient Power Supply Voltage
Total Load Resistance = 300 ohms
At 20 mA loop current, the voltage drop across the load(s) is 6 volts:
300 ohms x 20 mA = 6,000 mV or 6 volts
Subtract 6 volts from the 24 volt source to determine that 18 volts is
available to power the Model 692. The 18 volts is within the speci-
fied 16 to 40 volt range and is sufficient to power the transmitter.
EXAMPLE 2
Insufficient Power Supply Voltage
Total Load Resistance = 700 ohms
At 20 mA loop current, the voltage drop across the load is 14 volts:
700 ohms x 20 mA = 14,000 mV or 14 volts
Subtract 14 volts from the 24 volt source to determine that 10 volts
is available to power the Model 692. The 10 volts is below the
specified 16 to 40 volt range and is not adequate to power the
transmitter. If, for example, the power supply voltage was 40 volts
instead of 24 volts, the voltage available to power the Model 692
would be 26 volts, well within the specified range.
