EEVblog Electronics Community Forum
Products => Test Equipment => Topic started by: gridleak on September 17, 2014, 04:17:07 am
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I'm building a front end proposed some years ago by Conrad Hoffman in Poptronics, to turn an ordinary hand held DMM into a precision null meter. Any hand held with a 200mv or better range is a candidate. However, I anticipate that watching bobbling digits would not be as pleasant as having some analog representation of a null meter. I know that there are hand held DMMs with Analog Bar Graph. I don't own one, and therefore can't exercise the capabilities of such an instrument. Can a member of this forum point me to a particular hand held DMM whose analog bar graph can be programmed to act in "null meter mode"?
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The digital multimeters which I have that include a bar graph do *not* reset the bar graph when relative mode is used. The bar graphs always read absolute values however they *also* read increasing positive or negative voltages to the right so they do serve as sort of an absolute value null meter.
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Some meters display a Pos/Neg bar graph when in relative mode. The Fluke 87v for example using the zoom power up option.
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The UNI-T UT71 can also do it:
The main display shows the null deflection, along with the bargraph
The top left display shows the absolute value
The top right display shows the offset value
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Oh my, no free lunch for me. The fluke 87v goes for around the same price as vintage keithley 155 null meters being flipped on ebay. The ut71 goes for the same price as pre-flipped 155s were going for in august. I'll watch for an unflipped 155 for a couple of months, and if none, learn to live with the bobble.