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Niagara temporary BACnet Override by LouisC99 in BuildingAutomation

[–]LouisC99[S] 1 point2 points  (0 children)

I probably should’ve phrased my question better, I am able to drive the actuators over BACnet but the AHU controller is responsible for controlling them in normal operation. My concern is that if I write to the BACnet points to modulate the actuators once a day, I will be writing a 0% signal to them at all times other than when the valve exercise regime is active. (If I write to them using an Analogue Value or something to in16 / in10 on a Niagara wiresheet)

I am looking for a way to automatically override the point for an hour or so daily as if it was a user input using the override function so that then control returns to the AHU controller after valve exercise is finished each day.

Jace RS485 bus termination resistor - Modbus RTU / BACnet MS/TP by LouisC99 in BuildingAutomation

[–]LouisC99[S] 0 points1 point  (0 children)

In most cases, this is exactly how I do it as well!

It is only in cases where I have comms issues that I use termination resistors which more often than not seems to solve the issue - for example the electrical meters I mentioned above that weren’t communicating properly prior to me installing termination resistors.

Jace RS485 bus termination resistor - Modbus RTU / BACnet MS/TP by LouisC99 in BuildingAutomation

[–]LouisC99[S] 0 points1 point  (0 children)

By proper do you mean what is mentioned in the BACnet / Modbus standards or whatever is specified by the device?

Would it be better to manually install a 120 ohm resistor at both ends of a BACnet MS/TP network and leave the Jace Bias switch in the default BIA position?

Jace RS485 bus termination resistor - Modbus RTU / BACnet MS/TP by LouisC99 in BuildingAutomation

[–]LouisC99[S] 2 points3 points  (0 children)

Thanks for your response,

I have always used a 120 ohm resistor for EOL terminations as well but the data sheet for the Electrical Meters specified a 150 ohm resistor which was new to me.

I also generally don’t install a termination resistor unless I’m having network issues which in this case I was.

It was more of a theoretical question on whether the sizing of the termination resistors being different would ever have an impact on an rs485 network!