Orion System MODGAS II - Manual (Page 11)

MODGAS II Controller Section 1
Overview and Wiring 1-7
Board Inputs & Outputs
Analog Inputs
Input #1 - Heat Enable Contact (HEAT EN)
This input is only required when the controller is used in stand-alone operation; it is not
required when used as an expansion board to other unit controllers.The Heat Enable input
is activated by a 24 VAC signal supplied from a building automation system to enable the
MODGAS II Controller. The controller will not operate without 24 VAC being applied to
this input terminal when used in a stand-alone configuration.
Input #2 - Supply Air Temperature Sensor (SAT)
The Supply Air Temperature Sensor is the control source. This sensor has to be installed
for the unit to operate. The Supply Air Sensor is located in the discharge air stream and
monitors discharge air temperature to maintain the discharge air temperature setpoint.
Input #3 - Reset Input (RST IN)
The Discharge Temperature Setpoint can be reset by supplying a 0-10 VDC
signal to the RST IN low voltage terminal block. This reset signal is optional and need
only be used if you require resetting of the discharge air temperature.
Relay Outputs
Relay #1 - Fan Enable (FAN)
This relay works in conjunction with the LO SPEED relay to control the speed of the
induced draft blower motor. When the MODGAS II Controller has heat enabled, this
relay closes to bring the induced draft blower on at high speed. The controller will
activate the LO SPEED relay to reduce the induced draft blower speed as the gas valve
modulates closed.
Relay #2 - Fan Low Speed (LO SPD)
Depending on the gas valve position, this relay will close to switch the induced draft
blower to low speed. The controller automatically switches the blower to low speed as
the gas valve modulates closed in order to maintain proper fuel to air ratios.
Relay #3 - AUX Output (AUX)
If using EPROM SS0056 V 2.20 or higher, the AUX Output Relay is functional. Once
the MODGAS II Controller brings on heat, if the Supply Air Temperature rises 5˚F and
the valve output has reached 90%, then the AUX Relay will activate to bring on a 2
nd
stage of fixed heat. The modulating valve is then able to modulate as needed to maintain
the Heating Supply Air Setpoint. If the modulating valve falls below 30%, the AUX
Relay will disable.
Gas Valve Output (VOUT)
This output is designed to supply a 0-20 VDC output signal for control of the modulating
gas valve. Up to two gas valves may be connected to this output if required by the
application. Do Not Connect More Than Two Gas Valves.