Calibration of Timers to NIST - How are digital and analog timers calibrated?

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Marc

Hunkered Down for the Duration
Staff member
Admin
#2
Subject: Calibrating Stop Watches
Date: Sat, 18 Sep 1999 16:45:47 -0400
From: "Morrill S. Reynolds III"
Organization: Genzyme Corp.

Hello Marc,

I just stumbled across your website and one of your topics was calibrating stopwatches. We are looking at buying a device that measures the frequency of the crystal oscillator inside. There are no eye hand coordination errors etc. You simply place the timer/stopwatch on the device and it determines the number of seconds per wek or month it is off. It will work with quartz and mechanical type watches. The device model number is a Q Test 6000 and it is made by Witschi Electronics. They may be reached at 1-800-882-7977. We are currently testing the watches and timers we have by comparing them to a frequency counter. This device will save us a considerable amount of time. I just thought you may be intersted in it

Morrill Reynolds III
 

Jerry Eldred

Forum Moderator
Super Moderator
#3
I just read your post on calibrating timers and stopwatches. There are a few different methods to do this. The simpler method I have used involves first running an experiment with numerous iterations between the operator and the standard wherein you start the stopwatch and standard and the same time and stop the stopwatch and standard when the stopwatch reads exactly 10 seconds. Repeat this process at least 25 times (I did it 100 times for about 10 seconds each). Record the data and calculate a maximum deviation between readings. Add this to your measurement uncertainty as operator error. For a standard, use either a time mark generator (such as used for an oscilloscope calibrator) or other suitably accurate signal source. Use the start stop function on a frequency counter (I used a H-P 5335A counter). Set the repetition rate of the source to either 1 KHz, 10 KHz, 100 KHz or 1 MHz. Reset the counter readout to zero. Press start on the counter at the same time as pressing the start on the stopwatch. Let them run for an adequate amount of time (do uncretainty caluclations for the combined uncertainty of the counter, the signal source and the operator uncertainty), and allow enough time to minimize the impact of operator uncertainty. Be sure you get 4 to 1 or greater Test Uncertainty Ratio. When you stop both, be sure to look at the stop watch display to try to stop at a nominal (or close). Record readings, calculate deviations.

I do NOT recommend measuring the timebase in a stopwatch. You will get very mixed results, and MAY damage the stopwatch.

There is anohter method that I can look up if needed. Some nuclear industry contractors make up test fixtures that start the stopwatch and the standard at the same time. I have not been able to locate one of these.

You can email me at [email protected] for further questions.
 
E

energy

#4
Oven Process Timer

Having completed a search for "Timers" and thinking that some of the responses may be overkill, I would like to present the following from our Coating procedure for Pressure Vessels (Tanks), big enough to work in.

Gel Bake-275 Deg. F. 40 to 50 minutes....Depending on vessel configuration. Longer for vessels with false bottoms and/or portsights

Final Bake-360 Deg. F. 110 to 140 minutes...Depending on vessel configuration. Longer for vessels with false bottoms and/or portsights

We have (2) Honewell Digital Temperature Indicators to monitor and set temperature and a Process Timer that turns off the heat to the oven at the time you set it for. It has been proposed that we install a Bi-Metallic Thermometer at the point where the thermocouples are located to compare the meters. To satisfy a potential calibration inquiry. The thermometer would be in 1 or 2 deg increments, calibrated by an outside lab. We cannot afford to lose the time to get the equipment calibrated by an outside lab. They also do not want to purchase extra equipment to install during the time it would take for calibration outside. The timer would be checked against the electric clock nearby or somebody's timepiece. Don't laugh. The reasons given is that the time for baking and the varying temperatures are estimates arrived at through years of performing this process.
Can an Auditor question the methods proposed with such varying baking times and temperatures? The time would be +/- 2 minutes and the temperature would be +/- 5 deg.

Take it easy on me. :ko: :smokin:
 
R

Ryan Wilde

#5
Re: Oven Process Timer

energy said:

The timer would be checked against the electric clock nearby or somebody's timepiece. Don't laugh. The reasons given is that the time for baking and the varying temperatures are estimates arrived at through years of performing this process.
Can an Auditor question the methods proposed with such varying baking times and temperatures? The time would be +/- 2 minutes and the temperature would be +/- 5 deg.

Take it easy on me. :ko: :smokin:
Here is a TRACEABLE, FREE alternative, and you can do it yourself! First, go to
http://ts.nist.gov/ts/htdocs/230/235/105-5.pdf and download the NIST standard for stopwatches. Then, ftp to time-b.nist.gov/pub/daytime/ and get nistime-32bit.exe and download this handy little app that will set your computer clock to the NIST UTC timeserver (make sure you do it a few times to reduce the effects of 'net delay). Start your timer, run it 3 hours, stop it, repeat. Make sure you run the NISTime app before the stop and start for full traceability. There you go, no counters, only a computer connected to the net. Your uncertainty will be about 0.2 sec, with a tolerance (at least) ten times greater, so you'll be golden.

For your temp, I wouldn't use a bimetal, but there are some very reasonably priced digital thermometers (<$80) with a k-type thermocouple included. It is cheaper to have a digital thermometer calibrated, and they are much more accurate, so you're better off all around.

Ryan
 
M

M Greenaway

#7
Energy

Can you verify the coating after processing anyway ?

i.e. do you measure thickness, adhesion, etc ?
 
E

energy

#8
Yes

We measure thickness with an Instrument designed to measure coating thickness on ferrous materials. In addition, we apply apprx. 20,000 volts through a wire "Fan" in the interior lining to eliminate the possibility of having pin holes (holidays). This can occur if there is some porosity in the weld. As for adhesion, no. We know it adheres because we never had rejection due to peeling. There is a five year warranty on the lining and we have equipment that was coated in a previous life-same process-that has been in the field over 20 years. We are anticipating an Auditor witnessing the usage of instruments without any signs of Calibration or status. You know how you guys are!:p :ko: :smokin:
 
M

M Greenaway

#9
Energy

It could be argued that if you can verify the output of the process with calibrated equipment then you need not verify the parameters of the process itself with calibrated equipment.

For example we do not 'calibrate' in the strictest sense of the word the lead screws on our machine tools, or the dials on the slides, or the display of motor rpm, etc - what we do is measure the actual piece produced.

With such a large band on your baking times I would imagine that its unnecessary to calibrate a timer, any wristwatch should do the trick (verified with the bloke stood next to you if you wish).

P.S. Despite what Jim thinks good auditors would always consider the context in which the equipment is used in consideration of the effectiveness of the system in an internal audit - not just 'oh its measuring equipment it must be calibrated'.

Reminds be of that thread back along about calibration of a PC !!!
 
Last edited by a moderator:
E

energy

#10
I would hope so!

M Greenaway said:

Energy

It could be argued that if you can verify the output of the process with calibrated equipment then you need not verify the parameters of the process itself with calibrated equipment.

With such a large band on your baking times I would imagine that its unnecessary to calibrate a timer, any wristwatch should do the trick (verified with the bloke stood next to you if you wish).
That approach is what I would hope would satisfy an Auditor looking at 7.6 Control of Monitoring and measuring devices. Maybe it's my experience in anticipating questions that have caused problems in the past. Anytime you list a value in your procedure, it had to be measurable. If it doesn't matter, leave it out. Unless, like you said, there was a Final Acceptance Test that covered any sub-processes. We only verify that the lining is "Spark-Free" and the required thickness is there. Even the thickness tolerances are broad. For example: 20 to 40 or 40 to 60 mils thickness is the requirement. So how do we know that it is not under-baked/over-baked? (Fully cured). Only by adherence to the process which specifies values-no matter how broad, can we guarantee a consistant product. I just don't think there is any way around it. I wouldn't equate this with the calibration of computers. I suspect that you, being an Auditor Emeritus, would look at these three instruments and question their usage with an eye on what is their importance. Not seeing calibration stickers or instrument status on them is an open invitation for futher digging.

I once had a Gov't Inspector doing Final Acceptance Inspection on a sophisticated piece of electrical equipment. He tapped the face of each instrument used as test equipment. He asked, "Do you know why I do this?" Not overly impressed with him at first blush, I said "Not a clue." "Well, a few years ago I found a meter with the glass missing." You can only imagine what this highly skilled Quality Representative would say about a meter with no calibration status on it. Even instruments incidental to the process had to be labelled "No Calibration Required". The equipment could have been built upside down and he would not have noticed. But, he had the power/Final say. One has to be prepared to meet this this type of individual and ready to explain why things are not the way he/she imagines them to be. I'm not comfortable with allowing that opportunity. Heck, I may open the door to design validation or some other silly thing like that!:vfunny: :ko: :smokin:
 
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