EEVblog Electronics Community Forum
Products => Test Equipment => Topic started by: jsantoro on January 13, 2018, 08:47:52 pm
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Hi,
Just picked up this unit. I wanted an analog meter because I'm tired of staring at a DVM while trying to bias reel to reel tape decks. Anyway calibration on this seems very good (compared to a Fluke DMM). The input is a UHF type connector and a gnd terminal. If I attached a banana plug to the unit without either grounding it or attaching to a circuit the meter pegs hard. Do I need to use a shielded probe? The manual states you can use banana pus though.
Thanks, Jim
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Hi, which range have you selected ? This is a very sensible instrument with 1mV range and 10 M input resistance. Even with a shielded probe, I would not select one of the lower ranges without first attaching the ground and signal clips to the circuit you are measuring.
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It does it util the 3V range where it reads 1V with nothing connected to the probe. It's fine with no probe connected.
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I would say, that your meter is working properly. If you connect a wire to the magnetic pick-up input of your stereo and turn the volume control up, you will hear a strong hum (and maybe damage the loudspeaker). It is the same effect, the unshielded wire is picking the surrounding electrosmog and passing it to the amplifier inside your meter.
If the circuit under test has relative low impedance, a couple of banana wires may work. If the impedance is high, you will introduce hum in the circuit and false the measure.
I have a TRIO vt-106, the input resistance is only 1 M instead of 10 M. It shows 130 mV with an 80 cm wire connected to the input. A shielded probe shows just 6 mV.
The usual procedure to avoid violent movements of the needle is: 1) select a quite high range 2) connect the probe to the circuit under test 3) select the proper range and take the measure 4) select again a high range 5) disconnect the probe from the circuit
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Thanks a bunch Ferdie!