Why you want to thump a thermometer dial guage

[banjo]

For the first 12 years of my professional life, I was involved with the Instrumentation and Controls industry, primarily at Nuclear Power Plants.  (If any of you worked in this industry, drop me a line!), before moving over to software.

I calibrated a LOT of gauges.  I learned a thing or two about them.  I'm going to pass on one important aspect of using an analog (the simple dial gauge you may be using) - not to be confused with a digital gauge (which may use thermocouples or RTDs, etc).

You need to take a calibrated finger, preferably your favorite finger, and 'thump' the face of the dial of that gauge each time you go to read it.

There's a couple of reasons for that, some of which are interesting, and some of which are important.

The interesting first:  There's actually some friction involved, so that dial needle indicator is going to have a tendency to get stuck, if there's not a lot of difference in temperature involved.  So it's going to stick a little bit, then jump when the pressure difference caused by the temperature overcomes the friction.  It may jump 5 or 10 or 20 degrees, depending on the quality of your gauge.  

A 'thump' with your favorite finger will cause it to move past this friction point, and allow you to see the actual temperature.  I know, I know, for a bunch of you social rejects, you are gonna have finger envy, but that's just something you are going to have to deal with on your own.

The important information: When you thump that dial indicator, it's going to do one of three things:

• It jumps up.
• It jumps down.
• It doesn't move.

Each of these is giving you some important information about the trend of your temperature.  For the sake of this example, assume that you are at your desired temperature as indicated by your gauge, and then you thump it:

If it jumps up: then your temperature is trending up.  You may want to back down on your dampers a little bit.

If it jumps down: then your temperature is trending down.  You may want to open up your dampers a little bit.

If it doesn't move: then your dampers are set correctly.

So, it's REAL IMPORTANT to FIRST READ THE TEMPERATURE, then thump it, THEN READ IT AGAIN so you can an idea of the trend.

Happy Smok'in!

 

[pops6927]

Very true, one thing you learned very quickly in meat and deli-bakery too.  Your temps are your job.  If incorrect, and you trust it, you lose your job, real quick.

 

[forluvofsmoke]

Very good point, and something I had forgotten after leaving my safety supervisor/technician job nearly 13 years ago. I did a lot of analog pressure gauge calibration for supplied air and self contained breathing apparatus, as well as electronic gas/fire detection equipment calibration, trouble-shooting and circuitry repairs...all in/for the petrochemical industries (oil/gas reservoir development, production, gathering, refining)...8-1/2 years...fun job, but the pay wasn't worth spit back then.

One of the main things I do remember about analog pressure gauges is that they are most accurate at the mid-range of the gauge's reading...not sure if analog temp gauges act the same or not, but it may be true for them as well. For pressure gauges, there were usually three to four steps on the dial for calibration checks (zero check, 25-33%, 50-66%, 75-100%), depending on the application and manufacturer, but these were for high-pressure breathing air cylinders and compressors, breathing air supply pressure regulators with low (line pressure) and high pressure (supply cylinder pressure) gauges. None of these gauges had a vibratory recall mechanism, and you could notice minor pressure changes by bumping them. Average service temperature, severity of temperature peaks and valleys, storage and service humidity and air-borne chemical vapor/dust contaminants or dirty conditions, and the number of cycles and % of cycle range through the gauge scale reading all seemed to have an effect on their actual serviceable life...some gauges were designed to be more tolerant or less susceptible to environmental factors.

Thanks for the reminder, banjo!

Eric