Using the Analog Outputs
This control panel is supplied with an analog output for each relay board that can be connected
to a building management controller or variable-frequency drive. These outputs can produce
either a current or voltage signal that is proportional to the average concentration of the target
gas present at each sensor on a zone. By moving jumpers, located on the relay board, the
user can select from 4-20 mA, 2-10 VDC, 1-5 VDC, and 0.2-1 VDC signals. This signal is
available at the terminal strip TS9, located at the top right corner of the relay board. See figure
19 on page 58 for the signal mode selection jumpers.
The output signal is connected using a two-conductor shielded cable. The resistance of the
total cable length must be less than 250 Ω if the 4-20 mA current loop mode is selected. For
the voltage modes, the input impedance of the controller must be greater than 100 kΩ.
Ground the shield of the signal cable at the controller earth grounding point only to avoid noise
conditions created by ground loops. Although the positive signal lead can be shorted to
ground without causing damage, this condition should be avoided. Also, do not route the
signal cable in conduit containing other wiring to avoid unwanted noise pickup.
The analog outputs produce a signal based on the full scale response of the sensors. See the
graphs in figure 21 on page 59 of this manual.
As an example, a Brasch Carbon Monoxide Transmitter has a full scale output of 200 PPM
CO. For the 4-20 mA output mode with a single sensor configured, 0 PPM CO would equal 4
mA while 200 PPM CO would equal 20 mA. Follow the instructions supplied with your
controller to adjust the controller’s input for the proper scaling of the signal.
IOM03
Rev 1.1 – May 18, 2021
39
