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  Measurement, Test and Calibration
  Calibration of Timers

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Author Topic:   Calibration of Timers
Mitchell Medford
Lurker (<10 Posts)

Posts: 3
From:Black Mountain NC
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posted 27 September 1999 08:00 AM     Click Here to See the Profile for Mitchell Medford   Click Here to Email Mitchell Medford     Edit/Delete Message   Reply w/Quote
How are digital and analog timers calibrated?

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Marc Smith
Cheech Wizard

Posts: 4119
From:West Chester, OH, USA
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posted 28 September 1999 04:52 AM     Click Here to See the Profile for Marc Smith   Click Here to Email Marc Smith     Edit/Delete Message   Reply w/Quote
Subject: Calibrating Stop Watches
Date: Sat, 18 Sep 1999 16:45:47 -0400
From: "Morrill S. Reynolds III" -mreynolds@genzyme.com-
Organization: Genzyme Corp.
To: cheech@Elsmar.com

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

[This message has been edited by Marc Smith (edited 28 September 1999).]

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Jerry Eldred
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Posts: 136
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Registered: Dec 1999

posted 03 December 1999 11:55 AM     Click Here to See the Profile for Jerry Eldred   Click Here to Email Jerry Eldred     Edit/Delete Message   Reply w/Quote
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 rn0414@email.sps.mot.com for further questions.

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