What in the H*** is a dynamometer?

[sklimek]

I am currently looking at HP 330B distortion analyzers for two reasons, they are cheap on Ebay and the calibration is rather simple if you have a ‘dynamometer voltmeter’. I recently found one on Ebay and was wondering if anyone knows if this meter is usable for the type of calibration I need. Also, any good recommendations of a good source to check the calibration of the dynamometer.

From the HP 330B manual:

"Probably the most accurate method in the field to check the calibration of the voltmeter section of the Model 330B is a test using a cathode-oscilloscope and a freshly-calibrated dynamometer type voltmeter.

After any new replacement tubes have heated in the Model 330B, apply a low frequency (50-60) cps voltage simultaneously to both the voltmeter section of the Model 330B and the dynamometer type voltmeter. Readings of the two instruments should agree closely. Try another tube if necessary.

Next, calibrate the cathode-ray tube of the oscilloscope by applying a low-frequency sinusoidal voltage simultaneously to the dynamometer voltmeter and to the vertical-deflecting electrodes of the c-r tube. No horizontal sweep voltage should be used. Directions for connecting to the deflecting electrodes of the tube are usually given by the manufacturer of the oscilloscope. By measuring the peak-to-peak deflection of the c-r tube trace with a graph screen and by noting the reading of the voltmeter, the deflection voltage of the c-r tube can be quicklt determined. It is important that the voltage used to calibrate the c-r tube be essentially sinusoidal and free from harmonics".


Here is the Weston dynamometer voltmeter:

http://cgi.ebay.com/ws/eBayISAPI.dll...ayphotohosting

Think this meter can do the job??

[AndrewT]

Hi,
just guessing, but I think the dyna is measuring power to arrive at the accurate voltage reading. The clever bit is that it is calibrated for both varying signals and DC and should read exactly the same for a true sinewave(rms) and equivalent DC and a non sinusoidal waveform.

There should be a web site that can confirm something along these lines.

[lndm]

Can't help you directly, a dynamometer is commonly known as a device for measuring a cars power. It has resistive turbines and is usually built into the floor.

[Mark Kelly]

AKA true RMS voltmeter, eg HP 3400A and later HP 3403C

Although this is now accomplished by electronic conversion, an early and very accurate method was to actually measure the heating power delivered by the input voltage (buffered of course).

[sklimek]

Originally posted by Mark Kelly
AKA true RMS voltmeter, eg HP 3400A and later HP 3403C

Although this is now accomplished by electronic conversion, an early and very accurate method was to actually measure the heating power delivered by the input voltage (buffered of course).

Hi, would a modern RMS meter for example a Fluke 87 be capable of making this dynamometer measurmentas well?

Link to pic of HP 3400A, the manual on BAMA site.

http://www.inxs-inc.com/cgi-bin/menu..._prod&id=10494

Thanx!

[AndrewT]

Hi,
check the spec of the Fluke87 for AC sinusoidal and non sinusoidal waveform accuracy. It is the non sinusoidal that will give you the clue to it's performance. The frequency range will also be a guide.

[sklimek]

Originally posted by AndrewT
Hi,
check the spec of the Fluke87 for AC sinusoidal and non sinusoidal waveform accuracy. It is the non sinusoidal that will give you the clue to it's performance. The frequency range will also be a guide.

Thanks, I'll do that, with a little luck - things just got a whole lot easier for me...

Stan