I got this B&K 290 multimeter at a garage sale. It needs a little calibration. Most of the adjustment pots are marked but its not intirely clear how they are used. One pot mounted on the range switch is not labled. Anyone have the calibration instructions for it? Remove 1 to reply.
I have found that each pot is close to the function it controls (looking at the top side of range switch). One can always remember a setting, and move the pot 1/4 turn to see if the reading changes; then move it back. So if you wish to calibrate the voltage scale, apply a voltage known to a better accuracy than the meter, then tweak the selected pot as mentioned and go to the next one; when found you can adjust appropiately. The voltage calibration should be done first (above range switch); it seems to control current and resistance. The other control (below range switch) can usually be left alone (capacitance). Some meters have as many as 6 pots; upper left usually voltage, lower left usually capacitance; lower right (near thermocouple input) isfor temperature); have not fiddled with the others.
labled.
There's no capacitance or temperature on this thing. It's a 115 v powered solid state (FET I think)VOM All but one pot is labled., (+DC Cal), (-DC Cal), & (AC Cal). These are probable obvious (Bias Adj), (Bal Adj) I can only guess at these (Hi ohm Cal) not sure about this one. There's a Lo Pwr & Hi Pwr resistance function. it seems to affect zero. AC & DC voltage reads about 9% low A large zero adjustment is needed when switching between Lo Pwr & Hi Pwr but the reading is close. The zero pot is near the end of its rotation. John
Sorry, i was referring to hand-held DVMs. But it seems that you know what most of the pots are for. Anyone that designs a VOM that needs seperate + and - DC cal is profoundly stupid. And the AC cal could easily be "automatic" by using the DC measurement system / cal. Wierd to have two different power levels for resistance...
I think it has to do with providing enough current to turn on solid state devices. I don't remember where I learned this but supposedly some meters would falsely show a diode as open cus there wasn't enough current in the resistance circuit to turn it on..
No, it is not the current; it is the voltage compliance. There must be sufficent voltage to drive the desired current, for the diode to conduct in the forward direction. Note only germanium, silicon and schottky diodes work; LEDs do not. Hand-held DVMs seem to use about 1mA (some more, some less). However, one can determine diode types with 10uA or with 100mA. The 1mA is chosen, so that the voltage drop that is measured, is recognizable by savvy electronic technicians. A silicon diode conducts rather well at 1uA, but would have a voltage drop roughly 200mV less than that expected in "normal" circuits; if you read 430mV, you might think you had a germanium or a schottky diode (those would read much lower).
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