Proportional Output Thermostat

[toygasm4u]

Hey guys,
This is my first time here, this appears to be the largest assembly of engineering brain-power on the web LOL. Hope you can help with this one.

I'm trying to find a "stand-alone" thermostat controller with the following features, to control a very large recirculator fan:

*NEMA 1 or IP 10
*120VAC powered
*an operating range of 10~40 deg C
*4~20mA or 0-10VDC output
*programmable

I'm wanting to vary the speed of a VFD based on a change of temperature between 60 and 80 degrees F, and can't seem to find anything with a proportional band greater than 2 or 3 degrees F. I would like to stay away from RTDs for simplicity's sake... was wondering if anyone knew of a manufacturer or distributor of such a beast.

Thanks for any help,

 

[itsmoked]

More info please.

A little confusion here.. You are talking VFD at the same time as 120Vac... Not real common.

Actual motor HP and power type 3ph voltage?

Environment?

Controlled to temp? (operating range = ambiguous)

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[AFab]

http://www.omega.com/toc_asp/subsectionSC.asp?subsection=N05&book=Temperature

 

[waross]

I like these models. They have everything you want, and some models are addressable and controllable over the internet.
If you don't want to use an RTD or a T/C, you can use a temperature transmitter. I would mount the controller next to the VFD and mount the temperature sensor remotely.

http://www.omega.com/ppt/pptsc.asp?ref=CN77000&Nav=temp03

yours

 

[bklauba]

What could be simpler than an RTD connected to a programmed smart relay with drag and drop programming, like a Crouzet?

BK

 

[aolalde]

My opinion, you will not find a sensor simpler and accurate as compared to RTD's, (100 ohms @ 0 C for your application). Read the specs on the inputs for the controller proposed by waross.

 

[jraef]

Actually, a lot of VFDs have this capability built-in now, all you would need is a 4-20ma temperature transducer. Then you just select the transducer for the mounting and environment conditions of the air plenum of whatever space in which you are wanting to control temperature. Something like this if you want wall mount in a room; Omega EWS Series link.

Look for a function in the VFD programming called PID control or even just PI control. Most will allow you to adjust the setpoint either through the keypad or through a simple external potentiometer. If this is the only control loop associated with this system, that would be the way to go IMHO. Do you already have the VFD? If so, what brand/model and we can tell you if it can do this without an external controller.

If you need to have a display that lets you know what the set point is, many VFDs can do that also, but in that case it may be easier to just use the controller shown by waross.

Eng-Tips: Help for your job, not for your homework Read faq731-376

 

[toygasm4u]

Thanks to all for the input. This is actually for an outdoor application. The VFD is already installed, and is limited to only a 0-10 or 4-20 input. I've been searching quite a bit today for a simple pre-assembled "thermostat" like unit with a proportional output that would be usable. At this point, I think my only option is going to be something like an omega RTD/probe assembly, and one of their less complex temperature controllers; I may even dumb it down to just a couple of discreet outputs and some drive presets... blah.

This thing has to be as close to plug-n-play as I can get it for the installation people; I have little faith in "lectricians". I hate to think about a good ol' boy trying to scale current loops, but wish me luck!! Hopefully, the instructions I write will be good ones.. lol.

Thanks again for the input,
~M

 

[z633]

have you looked at using one of these

http://www.controlres.com/wispii.htm

 

[waross]

I haven't bought an Omega for several years but the last few controllers I bought had a power cord, a short thermo-couple and a small screwdriver included so you could play with it and set the parameters at your desk.
respectfully

 

[NEWFIEBOY]

There is a thermostat which is used on dairy farms to control the barn ventilation fans. These controllers are used to control the motor speed of a single phase exhaust fan motors based on the ambient temperature verses the desired temperature. I can not give you the manufacturers URL right now, but I should be able to find it for you shortly if this is the type of application you are interested in.

 

[toygasm4u]

Hey Newfie,
That would be great! Again, thanks guys for all your input!