What is 'guard' connection on LCR meter for?

Discussion in 'General Electronics Chat' started by tobyw, Apr 8, 2013.

  1. tobyw

    Thread Starter Member

    Mar 21, 2013
    37
    4
    After agonizing over various LCR meters, I have finally bought this UT612

    It comes with some surface mount tweezers, and an adaptor to slot components directly into the meter.

    However, it would be nice to use it with clip probes sometimes, especially with ferrite windings. And I have some clip probes which came with my Uni-T multimeter.

    The probe which comes with the LCR meter has three leads - pos, negative and 'guard'. I can't find anything in the manual about this 'guard' connection. Googling around for other models, it looks like the guard terminal is primarily for SMD testing, and/or noise suppression, but the word 'guard' is making me worried....

    Could anyone tell me

    1. What is the 'guard' connection? Why are there two?
    2. Can I still use the meter with just a two-lead pos/neg probe..and will it mean it's less accurate or does it mean I am going to blow the thing up by accident?

    Thanks :)
     
  2. #12

    Expert

    Nov 30, 2010
    16,252
    6,751
    The original meaning of Guard is a grounded circle around an input pin on a printed circuit board. It reduces surface leakage currents into really low current input amplifiers by grounding them. From this, you might derive that a lead labeled, "guard" would be a ground.

    Right now, I can't imagine how you would "guard" a component on the end of 2 test leads.
     
    tobyw likes this.
  3. tobyw

    Thread Starter Member

    Mar 21, 2013
    37
    4
    That sounds like it would fit with the idea of being intended to reduce noise when measuring.. do you think?

    Can't think what else it might be for.
     
  4. #12

    Expert

    Nov 30, 2010
    16,252
    6,751
    Yes...probably....up to a point...used correctly.
    We did one last month where a guitar amplifier had extra grounds all over the place and it caused current induced hum. Try to use one (1) guard connection. Only use 2 if it still isn't right, and that might cause problems.

    Practice measuring parts you KNOW. When you get that infallible, try something where the unknown is the part, not your method.
     
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