Need simple setpoint device for room temp

[LMDAVE]

I'm surprise what I'm looking for is giving me trouble, but it's basically a device like a thermostat to feed the setpoint to a PLC without the need of sensing temperature.

I already have a Vaisala transmitter monitoring temp and humidity in the room. The user just wants to set the setpoint.

I just want a simple LED device with an up and down buttons that basically outputs 4-20mA of the number selected. No ON/OFF relays, no input device, just a simple setpoint control panel, so they can set the room temp.

Anything I come across is way too complex for this application.

 

[rdrast]

How about a regular mercury bulb thermostat?
1 digital input. Done.

 

[LMDAVE]

I need a value to set the setpoint, not a dig input to say I need cooling. Its just a basic PID controlling room temp from the VAISALA to a johnson controller. I just want to be able to set the setpoint from a remote location without having an HMI station.

 

[John Soltesz]

What kind of PLC? Is the PID control done in the PLC? There are a bunch of ways to do it.
The setpoint could be related to an analog input, something like a potentiometer feeding into a DC volt input. Just relate the input to a scaled integer register going to the PID control block. How you will display the setpoint could be a process voltmeter that can be scaled the same as what you would do in the PLC. You would need a power source like 10vdc, a pot something like 5 or 10k ohms, a digital scalable volt meter that needs a power source (24vdc, 120vac?). I would look at a small HMI that could be the same cost without much messing around.

 

[LMDAVE]

Yes, that's all I want is like a potentiometer setting the setpoint but it has to be digital, not a pot. The PID is already set, the transmitter is the PV, the controller has a setpoint already. I just want to use one of my analog inputs to have a remote device set the setpoint.

something that would look like this: (the omega unit only has relay outputs)

but I dont' want temp input on it, I just want it to be able to adjust a number (say 0-100), and have that number scaled 4-20ma and sent to an analog input. Just a simple LED device to set a value to a PLC.

 

[Lare]

http://******/1yT9xbm

Beka has device like that or you can build your own with couple resistors, pot and display

 

[RDS]

http://www.dartcontrols.com/product-guide/digital-analog-control-systems/

 

[boneless]

Something like this?

http://www.prelectronics.com/products/displays

They are actually pretty pricey.

For something pretty similar, we opted for a small HMI instead:

http://www.beijerelectronics.com/web/web_en_be_com.nsf/alldocuments/7997E41B9D7849EAC125794C002C94CF

 

[LMDAVE]

Boneless, I think those are display unit reading a value.

RDS, that is close since it's used to control speed I could have made it for setpoint, but the connetions looking dedicated for a VFD.

I decided to go with what I used in the past for this. It senses Temp and humidity and allows you to set the setpoint for each, and outputs all four: temp value, humidity value, temp setpoint, and humidity tempoint. I really just wanted to do a temp setpoint and that's it, but I'll use this since it is going in a clean room enviornment anyway.

http://www.veris.com/Item/HT2NAS0.aspx

 

[boneless]

You can set an analogue output on them to.

The piece you picked is pretty pricey as well, why not go with a small HMI?

 

[LMDAVE]

Because the VAISALA temp humidity transmitter I was going to have in that room is well over $1000, I'm going to drop installing that transmitter and use this VERIS for everything now. So, actually I'm saving money.

 

[boneless]

Well sure, if you compare it like that .

I do like the fact that it is one unit that does it all.

For your reference:
http://www.ebay.com/sch/i.html?_odk...+4+mA.TRS0&_nkw=humidity+sensor+4+mA&_sacat=0

 

[TConnolly]

Get a Nematron Optimate OM413. It is a $140 simple HMI that allows the display and setting of up to four setpoints and works with most PLCs.

You can get direct from Nematron or AutomationDirect.com also has them.


http://www.nematron.com/products/industrial/optimate.html

 

[shooter]

Get google to search for XTR105.
Use one to get a temperature to 4/20 mA
use another one also to read same temperature, however now the Pt100 is in a wetted sock this will give you the wet bulb temperature (with some calcs you can get the RH.
and use a 3 to have a potmeter set
when using a potmeter of 25 ohms and a resistor of 100 ohms
you will have a homemade thermostat for around 25 euro (and still very precise better as 0.1 C.
1000 euro for a thing i can make for 50 bucks.