Is that HVAC static test behaviors possible?

[jumacao]

The attach graphs is the results I received from a static test for areas of a room (Same HVAC unit). Is that HVAC static test behaviors (no changes for hours in temperature when measuring at .01 instrument readability) possible?

 

[MikeHalloran]

It looks like your equipment was sampling *something* every 15 minutes, and had a resolution in amplitude of 0.1 or 0.2 *somethings*, and whatever produced the graphs used a simple straight line interpolation.

I don't see a '.01' anything in there. Maybe accuracy, but not resolution.

If you sampled more often (and collected much more data) the traces would probably look much noisier.

I'm guessing the blue traces are temperature in degrees F and the red traces are RH. I think RH transducers respond pretty slowly. It appears the resolution of (your ADC for) that channel was set to 1 pct. ... is that the '.01' you were talking about?



Mike Halloran
Pembroke Pines, FL, USA

 

[jumacao]

According to data the first graphs was maintain at 71.77 F for 24 hours with only one hour exceptions. Is hat possible or normal to control a room temperature at .01 units for hours?

 

[jumacao]

when I says 71.77 I mean exactly 71.77 F

 

[MikeHalloran]

Uh, no. That's not how sampling works.

The room could have gone to -60 or +120 or any other number, while you weren't looking at it.

That's not how digital measurement works, either. It could have actually wandered around between 71.6 and 72.4 and you would never know it, because you clearly don't have two decimal digits of resolution.






Mike Halloran
Pembroke Pines, FL, USA

 

[jumacao]

Data have two decimals of resolutions, raw data have two decimals of resolutions. They present an exact two decimals fixed for many hours. I am just wandering if data was manipulated.

 

[MikeHalloran]

Intentionally manipulated? Probably not.
But I think you are misinterpreting it.
No offense intended.

Suppose you suddenly put the same transducer in a fridge, and measured its output at 5 second intervals. I suspect you'd see a stairstepped curve, and the first step below 71.8 would be around 71.2. No matter how many digits it's reported to, the measurement resolution appears to be somewhere around 0.6, maybe 0.5. It just happens to have not been calibrated to change from one value to the next on a nice integral number.


We're nearing the limits of my expertise on instrumentation, and you need more help than anyone could give you here. You need to read up on this stuff, or get help in the same room with you.



Mike Halloran
Pembroke Pines, FL, USA

 

[vpl]

jumacao

The question you need to be asking is what is the graph actually showing you. As Mike Halloran pointed out, the graph shows that the sample was only measured once every 15 minutes. However, I have known of instances where the data was taken more often but what was recorded (and so presented on the graph) was an average value. I have also run across cases where the instrument is capable of reading a much more accurate value than the recorder was capable of reproducing.

Also, as Mike Halloran again pointed out, your graph does not show what the red and blue lines represent. Without knowing that, it's very difficult to respond in any meaningful way.

Patricia Lougheed

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[RossABQ]

If this is for a cleanroom certification, i.e., a room with a great number of air changes per hour, and industrial controls, static conditions will produce a very low variation. If it's an office with low air changes, and commercial quality controls and control devices, you would not see this flat of a graph. Can you give some more information?