Multimeter Connector

Discussion in 'The Projects Forum' started by Ally Cat, Apr 20, 2016.

  1. Ally Cat

    Thread Starter Member

    Mar 28, 2016
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    I am currently working on a Digital multimeter design and I am looking for a connector to select appropriate voltage rating, as well as resistance measurement and other multimeter functions. I need a rotary 12 position 2 pole connector to achieve these ends. I found the PLR series which only handles voltages of 250 AC and .15 A. Now I could bypass this for the current measurements but I really can't for voltages exceeding 250 V and I really don't want do it for the current draw selection. How do multimeter designers deal with the high voltage coming in on the rotary switches. Is there a switch out there that can handle greater voltage and currents?
     
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    They use the pcb and etch the circuit out on it, as for current they use low resistance shunt wire links.
     
  3. Ally Cat

    Thread Starter Member

    Mar 28, 2016
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    Thanks Dodgydave

    I am familiar with the low resistance shunt. The problem I encountered is all of the rotary connectors have only about hundred or so milliamps on the rating and the current rating is at 10 A on most DMM. There is example of this some where in All About Circuits forum. They us a 120 voltage Radio Shack Rotary switch to toggle the DMM.
     
  4. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    Multimeters dont switch current, you have to swap the positive lead in a different socket, the rotary switch just selects a different resistor chain to tap the voltage across it.
     
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  5. Ally Cat

    Thread Starter Member

    Mar 28, 2016
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    Thanks Dodgydave

    That answers one question but how does the connector handles the voltages in the 1000 range, albeit at very small current due to the resistor chain.
     
  6. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    If you open a multimeter up, the sockets are usually soldered to the pcb directly or hard wired with heavy duty wire,...
     
  7. Ally Cat

    Thread Starter Member

    Mar 28, 2016
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    I sorry I don't understand how that affect the connector rating. The voltage must pass through the connector. Or is there something that I missing?
     
  8. Marcus2012

    Member

    Feb 22, 2015
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    Electrical arcs don't usually become a problem until you go past 1000V, anything beneath this is generally considered low voltage and shocks rather than arcs are the main concern. You will find that your probe cables are rated for a maximum voltage, a breakdown voltage (1000V for cat 2 iirc) which shouldn't be exceed or the insulator will experience dielectric breakdown and will become a conductor. Connectors, cables, probes and discrete/passive components will always have a breakdown voltage noted in the manufacturers datasheet.
     
  9. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    Any component thats exposed to 1000V MUST be rated for 1000V+.. plain and simple.
    If the connector you found is not then move on and find another..
    Every multimeter I've ever seen has used "banana jacks"... most carry a high voltage rating. 7kV,etc... (Pomona is one of the popular brands.. there are many others)
    Not sure why you aren't just using those.. Then off the shelf leads,etc.. will just plug right in..

    But I'm a bit confused by your usage of "connector" and how its going to be used for selection of resistance/voltage,etc..... Do you mean switch? or do you just mean a connector that plugs into specific jacks on the front like any regular meter
     
  10. hp1729

    Well-Known Member

    Nov 23, 2015
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    PLR? Primary Latch Reinforcement? "Rotary Connector?" or Rotary switch?
     
  11. Ally Cat

    Thread Starter Member

    Mar 28, 2016
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    That is my understanding as well. A rotary switch is what I am looking for. I can see now how I confused you. I can't seem to find one that is rated for 1000 Volts needed to handle the voltage necessary for this DMM to work. PLR is a series of rotary connectors that I did find and it seems to be the closest I can find. It fails to archive the minimum of what is available on the market in DMM's.
     
  12. hp1729

    Well-Known Member

    Nov 23, 2015
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    Avoid passing the 1,000 V through the switch. Voltage divider first.
     
  13. Ally Cat

    Thread Starter Member

    Mar 28, 2016
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    The problem with that is the voltage divider will be in place weather the voltage is there or not. So when I am using the device to measure resistance or connectivity the divider will still be there. All schematics I have seen go directly into the connector. Unless there is something that I am missing.
     
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