Contemporary Control Systems BASremote User Manual (firmware 3.1.x) - Manual (Page 26)

TD040300-0MF
26
When measuring current, remember the BAS Remote sinks current to ground. A 250 Ω
impedance is effectively applied between points A and B on the input. To measure
current, it must be driven into point A with respect to point B. For two-wire current
transmitters, the more positive point on the transmitter attaches to the +24 V on the BAS
Remote loop supply or it can attached to an external loop supply as long as that loop
supply has a common connection with the BAS Remote. The less positive connection
is made to point A on the input.
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 BAS
Remote 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.
5.6 Analog Output
Either voltage in the range of 0 –10 VDC or current in the range of 0–20 mA can be
outputted by assigning analog outputs. Configure an output using a web page. Select
the appropriate range. For DC voltage, the output voltage is applied to point A with
respect to common. For DC current, the output current is sourced from point A to
common so there is no need for a loop supply. A current output can
source up to 20 mA into a resistive load not exceedin
g 750 Ω. Verify the
burden that a current output device will present. The BAS Remote cannot
generate enough voltage to drive loads with higher resistance.
Figure 12 — Analog Output Connections
Figure 12 illustrates connections to a three-wire damper actuator. The damper requires
a 0
–10 V command signal which can easily be accomplished by the BAS Remote.
However, if a current output is desired it is possible to set the BAS Remote analog
output to 4
–20 mA and install an external 500 Ω resistor that will convert the 4–20 mA
signal to 2 –10 V.