paint audit questions

Date 11-15-2013 13:49

Curious if anyone uses a sling pschometer to measure dry bulb/wet bulb temperatures?
If so what do you do about annual calibration of the instrument?
I'm looking for a way to verify the accuracy in-house vs sending it out for a sticker by a 3rd party.

I had several electronic units that did an excellent job and those were sent back to the mfg annually for calibration...however, the paint department here is really hard on instruments and it costs as much to repair this as it does to purchase a new one and we've been down that road several times already...so it's in my drawer and I resorted to using the sling psychrometer and weather charts(there is one that I created and posted in Useful Downloads built in Excel) to figure the dewpoint and relative humidity.

By CWI7611 (**)

Date 11-16-2013 15:24

I have used a sling psychrometer years ago and they worked very well. With that instrument as long as the thermometer isn't replaced I don't know what kind of calibration is required. I guess it keeps the paper trail in order.

I like the electronic units much better. I think periodic calibration (at least annually) would be preferred. Some people never calibrate them.

With management's support (if you can get it) tell the knuckle draggers in the paint department to be a bit more careful or you will reject any paint jobs you find where they have used a damaged psychrometer. Get management to allow you to bill or transfer the costs for the repairs to the paint shop. Easily said, huh? Paint department gets you to repair/recalibrate them, saves them money, lower budget, better efficiency, I as a supervisor get a better raise.

By jwright650 (*****)

Date 11-16-2013 15:37

Yeah the Sling psychrometers from KTA Taylor are around $90-100 and they haven't broken any of those, the electronic ones we had before were $1400-1500 and nearly that much to replace the probe that sensed the surface temperature to figure the delta between the dew point and the surface temp. About the only thing that has worn on the sling psychrometers have been the hinge where they clip on and spin(plastic with a metal pin)....so I'm sticking with the $100 sling psychrometers for now. Previously I was trying to make the paint guys lives easy and gave them every tech tool they needed to make recording this data easy, but I'm at a point with them now where I'm not too concerned about all of that.

By jwright650 (*****)

Date 11-15-2013 15:42

Not yet. KTA Taylor

http://www.ktagage.com/Product_Taylor_Sling_Psychrometer.asp

By jwright650 (*****)

Date 11-15-2013 16:41

http://www.paintsquare.com/education/branding_images/JPCL_Web_Corbett_Ambient.ppt

According to this^^^ it mentions removing the sock from the wet bulb thermometer and comparing it to the dry bulb...and it also mentions comparing it to a known calibrated thermometer. I need to purchase ASTM E337 to see if it has any additional info aout verifying the instrument.

just an FYI for other reading this:

ASTM E337 - Standard test method for measuring humidity with a psychrometer
ASTM D7091 - standard practice for non destructive measurement of DFTs,<snip>
ASTM D3276 - standard guide for painting inspectors (metal substrates)

By eekpod

Date 11-18-2013 11:23

We only use digital, no sling.

By G.S.Crisi (****)

Date 11-18-2013 23:21

Sling psychrometer and psychrometric chart are part of my lessons at Mackenzie Presbyterian University in Sao Paulo. I bring a psychrometer into the classroom and distribute a chart to every student. I ask one of them to read the dry and wet bulb temperatures and then I order them to find out on the chart the following air properties:
Absolute humidity
Relative humidity
Enthalpy
Specific volume
Density.

The psychrometer is used for teaching purposes: to explain the students how to use it and what can you expect from it. To say the truth, I'm not very concerned about its precision. An error of a couple of degrees Celsius won't prevent the students from understanding how it works. The psychrometric chart is very good: it has been published by Carrier Corporation. Every year I give a telephone call to their Brazilian subsidiary and they send me (free of charge, of course) 30 - 40 copies.

Giovanni S. Crisi
Sao Paulo - Brazil