Contemporary Control Systems BAScontrol20 User Manual - Manual (Page 15)

TD100700-0MB
15
4.2 Universal Input
— Configured as Analog Input
An analog input can measure voltage in the range of 0 –10 VDC or it can measure
current in the range of 0 –20 mA with a 500 Ω external resistor. Transmitters that
produce an elevate d “zero” such as 2–10 VDC or 4–20 mA can be measured as
well. Using the web page, configure the input for voltage. When set as a voltage
input, the input impedance is 1 MΩ.
With voltage measurement, connect the more positive voltage to point A and the less
positive to common C as shown in
Figure 4 . On three-wire devices such as damper
actuators, the output signal is referenced to the damper’s power supply common.
That common must be at the same reference as the BASC20 common. Notice the
connections in the diagram. In this situation it is only necessary to attach the
transmitter output to point A on the BASC20 input.
Figure 4
— Analog Input Connections
When measuring current from two-wire transmitters, remember the BASC20 sinks
current to ground. A 50
0 Ω resistor is applied between points A and C on the input.
To measure current, it must be driven into point A with respect to point C.
Care should be exercised when connecting to a three-wire current transmitter.
These are usually non-isolated devices between the power source and signal output.
The BASC20 will sink current from its input to ground so the transmitter must source
current from a positive potential to ground. If the three-wire transmitter works in this
manner, it can be accommodated.
Four-wire transmitters usually have isolation between power supply and signal
output so their output stage can usually be treated as a two-wire transmitter.