representative of the threshold concentration of target gas. See the tables on page 7 for the
gas concentrations represented by each position. Note that the switch assigns threshold
concentrations for both gases in the zone. Separate sensors of different types into different
zones to adjust the threshold concentration by gas. The High Alert setpoint cannot be
adjusted.
High Alert Relay Operation
There are two sets of contacts for the High Alert relay in each zone. The main contacts are
labeled “A2 NO” and should be used in most scenarios. This sets the High Alert relay to close
upon reaching the threshold concentration, thus activating any connected ventilation
equipment. In fail-safe mode, this relay will open so as to prevent malfunctions with 2-speed
fan configurations. Moving the wire to “A2 NC” will cause any connected equipment to
deactivate upon reaching High Alert and activate in fail-safe mode.
Fan Speed
The operation of the relays to accommodate different types of systems can be adjusted by JP5
and JP10 on the left side of the control board. Placing the jumpers on the top two pins will set
the relays to operate for a 50/100 system while placing the jumpers on the bottom two pins will
set the relays to operate for a 2-speed system. Fan 1 controls Zone 1 and Fan 2 controls
Zone 2, but in most cases, these jumpers will be set to identical positions. See figure 9 on
page 43 for details.
Proportional Output
To adjust the output, set the jumper at JP2 on the bottom, right of the sensor board to the
desired unit – “Volts” or “mA”. Then set the jumper at JP3, just above JP2, to the desired
output signal – 2-10 V, 1-5 V, 0.2-1 V, or 4-20 mA. Be sure to follow the instructions below to
ensure proper functionality of the proportional output.
Using the Proportional Outputs
This Brasch Gas Detector is supplied with a linear proportional output for each sensor 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 concentration of the
target gas present at the sensor. By moving jumpers, located on the sensor 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 TS3, located at the bottom right corner of the sensor board. See figure 13
on page 45 for the terminal strip locations and signal mode selection jumpers.
IOM01
Rev 1.0 – December 22, 2020 27
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