pnuematic thermostat calibration????? 1

[kaukau]

Hello gang, I have a question about calibration of pnuematic thermostat. Can someone please tell me the proper way to calibrate pnuematic T stat.
thanks

 

[imok2]

You must first determine the final actuater spring range
EX. if the spring range is say 3-13# then the range is 10#, so you would calibrateto to mid position or 3#+5#= 8#
The 3# is the start position on the spring and the 5# is the mid position on the spring, once this has been established, you need to set the stat at the room measured temperature then adjust the branch line pressure to the actuater to 8# you are now in calibration, now you can set the stat at the correct temperature you want to maintain

 

[tombmech]

Throw it away and get something digital. ;-)

 

[Ashereng]

pneumatic temperature controllers (thermostats) are very common in remote location without power.

A digital thermostat does not work without power.

"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?

 

[tombmech]

Have you familiarized yourself with smiley faces that are blinking? That is described in detail in item #9 in the FAQ's you helpfully cite.

On the other hand, I spent a large portion of my career replacing antiquated, pneumatic controls with DDC components. Replacing instead of repair became enough of a theme that management eventually accepted it as a justification - "If it's pneumatic, we have to throw it away - it costs too much to continue to repair and/or calibrate," for instance, could be a successful strategy.

I've also designed and installed several solar-powered, cellular phone equipped monitoring sites at remote locations on a large-property facility - where power nor wired-communication infrastructure was available. I submit that is a better alternative than worrying about re-calibrating a pneumatic sensor in most instances.

The statement I made could have been valid in many contexts. Sorry if you interpreted it otherwise, Ashereng.

 

[tombmech]

Ashereng,
I see from other posts that you have the "FAQ" included in your regular signature. My bad for thinking it was specific. Please accept my apology for thinking otherwise. Mea culpa.

 

[Ashereng]

No apologies necessary.

I agree that pneumatic controllers have in recent times (last 20-30 years?) been on the decline.

Pneumatic controllers, although it's been around for a LONG time, isn't antiquated. It has its specific strengths and usages.

I am not sure where kaukau's application is since it wasn't mentioned, but it could easily be in a remote location. A lot of my wells and tie-ins are located in the middle of nowhere.

In my industry, especially the upstream sites, they are still going very strong. Solar power is not always a solution for many sites. For many sites, the power would be from a propane/NG bullet/line and TEG. Although more reliable, they are more costly than solar. Hence, pneumatic/hydraulic solutions.


I agree, in a powered location, they are no longer used. In remote areas, they are great. Not only no power required, they are easier to understand. The logic is more "mechanical" and there to see. With a "electronic" solution, the logic isn't always as evident.

If you haven't taken a look a pneumatic controllers and equipment in a while, you may want to. Even if you won't be using them, I still think they may be worth a look, just for information.

"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?

 

[imok2]

From a teaching perspective I find that the student who is introduced to pneumatics first seems to grasp DDC much better. As was mentioned by Ashereng, the logic is there to see, so we teach both. And of course you have the Hybred system where both are used. I believe that there will always be a place for pneumatics in some capacity

 

[gregha04756]

Assuming the pneumatic device can be replaced with electronics, how should the electronic one be calibrated? This is not a facetious question, I work with digital thermostats, specifically BACNet compatible ones used in DDC. I "calibrate" the 'stat with a digital thermometer (which itself has to be calibrated), but this does not seem like a proper method. Any suggestions?

Thanks,

Greg Hansen

 

[Mechya]

First you need to determine the throttling range required (ie min. to max. temp. required) in your case the air branch pressure from the thermostat is assumed to be 3-13 psi for the the control system.

Next measure the ambient temperature near the sensing element of the thermostat.

Turn the setpoint knob of the thermostat to the ambient temperature.

Turn or manipulate the calibration screw in the thermostat until the branch line pressure is zero psi.

Then turn the calibration screw in the opposite direction until the branch line pressure is mid value of the 3 and 13 psi, in our case (3+13)/2 or 3+5 = 8 psi (5 is the midpoint of the range of 10)

Verify the throttling range referring to the earlier establish min. and max. temperature required. Fine tune the range at this stage and recalibrate as required.

Now your thermostat is calibrated , turn the knob to the desired value.

I hope this explains the process...