Temperature control button with 4 - 20mA or 0 - 10V

Hi guys,

Currently we are working on a project for a factory where they have rooms (50++) which required a wall mounted digital or analog switch. These switches must be able to control the 4 - 20 mA or 0 - 10V to the PLC (Siemens).

Meaning when the temperature is low (cold), the people at the room will turn the knob or jog the control button to increase the value send back to the PLC (by 4-20mA or 0-10V) and vice versa.

We prefer hardwiring or Profibus rather than any other network. The average distance from the control button to the PLC is around 80meter. We try not to use touch screen in every single room due to cost reason.

Any of you guys come around this kind of devices or other better solution.

Why so complex?
Why not use conventional residential wall thermostats ? that are really cheap?

A wall thermostat's output is a binary switch:
closed = call for heat
open = no call for heat

Then your I/O board is a high density DI card, not an AI card.

A wall thermostat is a little bit more complicated than a simple switch, but its still the best approach.

A conventional wall thermostat has a feature built in called a heat anticipator. When the furnace is running the small amount of current running through the switch contacts also heats a bi-metallic spring. Since the heat transfer rate from the room air to the bi-metallic spring lags the rise in room temperature, this feature "anticpates" that temperature lag and compensates for it by heating the spring. Some thermostats allow adjustment of the heat compensator. Some conform to a standard model. Modern digital thermostats "learn" the room lag and electronically anticipate the heat rise.

So you will need to model the lag for all your rooms and add your own heat anticipator to any analog signal you send back. Or you could do as Dan suggested and use a wall mounted thermostat.

The wall mounted thermostat has another advantage: Everyone knows how to operate it.

danw, Alaric, thanks for your info, if i understand correctly, the wall thermostats only gives "1" or "0". The room temperature (FCU) is controlled by the Siemens PLC (existing design) & monitored in the SCADA. I think the SCADA will not be able to capture the setting of the room temperature by using thermostat, thus the room temperature cannot be accurately control. Correct me if I'm wrong.

OK so you want
1. a central computer or PLC to monitor and control temperature in 50 rooms.
2. Ability to have person come in and turn a switch to call for heat or cooling

YOu could do this with occupancy sensors or even better CO2 detectors to detect presence and how much heat or cooling and makeup air to provide based on occupancy.

Dan Bentler

leitmotif said:

OK so you want
1. a central computer or PLC to monitor and control temperature in 50 rooms.
2. Ability to have person come in and turn a switch to call for heat or cooling

YOu could do this with occupancy sensors or even better CO2 detectors to detect presence and how much heat or cooling and makeup air to provide based on occupancy.

Dan Bentler

Click to expand...

Dan,

Yes, you are right. The person in the room can adjust the temperature as they wish at the temperature control button (i'm sourcing for).

We do have CO2 sensor, but that's for quality of the air, if the quality drop, the makeup air will supply more into that particular room.

Guys,

We managed to source for this dimmer switch which generate 1 - 10V output. Do you guys think it's suitable? I've not use any of this before, appreciate if any with experience with this device can enlighten us.

Thanks.