The client requested the following functionality,
- Thermistor input to produce a 0-10 volt output to control a heating valve over a 4 degree centigrade band with the set point adjustable in software.
- Thermistor input to give a relay output with a set point adjustable in software.
- Input from others via software to give relay output for system on/off.
- Input from others via software to give 0-10 volt output to vary fan speed.
- Digital input to give a common fault signal to be sent via software to others.
A BAS Remote controller from Contemporary Controls was specified and the inputs and outputs defined as follows,
SP1, SP2, Fan, Damper and Fault are all ModBus register addresses acces by a Trend Supervisor.
The follow diagram shows the logic strategy developed for the controller.
The control was wired in to a distribution unit and wall mounted in the plant room.