| Products > Test Equipment |
| Hacking the Victor VC-921 |
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| indman:
Yes, I agree! I would make in addition some more buttons on the front panel of a multimeter, for example, MAX/MIN,hFe, but is very difficult to find the empty seat in this miniature casing. :D |
| tronde:
I think you must add some more circuitry and probably make some changes to the rotary switch if you want hFE and current modes. The data sheets show some examples. Another thing - you have extended the counts to 10000. I have read that the AC/DC converter is a digital signal processor, and that it will fail if the measured value is above ~12000 internal counts. A pure sinus will have 14142 internal counts for 10000 counts AC voltage. This should give that a pure sinus ACV of more than ~8485 counts will show some error. Have you tested this? |
| indman:
No, I didn't test in details the ACV mode. I work generally with the mode DCV therefore I was interested in operation on measurement of constant voltage more in case of 10000 counting. Besides it is necessary to remember that there is the known problem of this update - in case of 10000 counting automatic switchings of limits only about 400 Hz correctly work in the ACV mode. If alternating voltage with a frequency over 400 Hz or there are high-frequency harmonicas, then the automatic machine works not correctly. It is in that case expedient to transfer to a manual choice of limits. |
| tronde:
Inspired by hgg in the UT-210E tread https://www.eevblog.com/forum/testgear/a-look-at-the-uni-t-ut210e/msg1058296/#msg1058296 I did som testing with an modified and an unmodified VC-921. I used 60Hz sine. The modifed (8000 counts plus added functions) shows some strange behaviour in the 800mV range (06H). The unmodified instrument has 400mV native. Between about 150mV and 500mV it shows some 5 - 10mV too much, decreasing at higher value. I have added the 80/800mV ranges as well (02H). No errors there. The unmodified VC-921 did not show any errors in the native 400mV range. Anyone experienced something like this with their hacked VC-921? |
| indman:
--- Quote from: tronde on September 15, 2016, 09:58:37 pm ---A pure sinus will have 14142 internal counts for 10000 counts AC voltage. This should give that a pure sinus ACV of more than ~8485 counts will show some error. Have you tested this? --- End quote --- Hi! I checked operation upgraded (9999 counting) multimeters of VC-921 and HP-890CN in the ACV (mV) mode. From the generator the sine signal with a frequency of 60 Hz is measured. Video can be watched according to this link https://yadi.sk/i/F2N06kz9ybS4v |
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