Rev 3.1 01/11/23 - 22 - Model 600 User Guide
5.8 Hydrogen Alarm
The system will enter hydrogen gas alarm mode when the input is active for 5 seconds. When this input
is active, the controller will enable emergency vent mode on both HVAC units. Both units will remain in
vent mode until the hydrogen gas alarm input is off and then will return to normal operation mode. An
alarm message will be displayed on the front panel along with status via Modbus.
5.9 Generator Running
The system will monitor the generator for running and display an alarm message if the generator
running input is on for 5 seconds along with status via Modbus. When the alarm is active, the Model 600
will disable operation of the HVAC systems based on the system defined function. The option is to
disable econ mode for both HVAC units or operate both units normally.
5.10 Communications Loss
If the Model 600 is defined for Modbus communications by changing the Modbus address from 0 then it
will monitor for communications on the serial port. If no communications have been received for two
minutes, then any remote commands previously sent will be ignored and the system will go back to local
operation. A message will be on the display indicating communications loss.
6 Remote Communications
The Model 600 may be programmed using either the keypad and display or through the Modbus serial
interface. The keypad can also be locked out to require remote programming only. Before
programming remotely, you must set the address and baud rate of the Model 600.
Review the Modbus map (appendix A) for the available registers and functionality.
The Model 600 will accept writes to certain registers from a remote agent. Some of the registers being
written to are only used while the unit is communicating. When communications are lost for two
minutes, the Model 600 will revert to local control mode. This section will discuss those registers that
can be set remotely but return to local default when the unit is reset or communications are lost.
6.1 Controlling Temperature
The controlling temperature register is holding register 100. This register will show the value of the
sensor(s) being used to make control decisions. For example, if the Model 600 has two zone sensors
and is configured to average those sensor readings, then the value of register 100 will be the average of
those two sensors. This register can also be written to by a polling agent to change the value of the
controlling temperature. An example of this function would be to calculate the average of multiple
sensors connected to other devices and then set the controlling temperature based on that average.
6.2 Outside Air Temperature
Modbus holding register 101 is used to tell the Model 600 what the outside air temperature is so that
the unit can determine if economizer mode can be used. This register would normally display the value
of the outside air temperature on the Model 600, but this register can also be written to so that a single
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