Looking at options for test boxes.

Discussion in 'Armory - Q&A' started by ktinoue3, Jan 16, 2017.

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  1. brtech

    brtech Podium

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    There are two basic ways to regulate voltage: a "shunt" or "linear" regulator (most 3 pin regulators are shunt regulators) and a DC-DC convertor.

    The shunt regulator requires a greater input voltage than output voltage and acts like a variable resistor whose resistance varies to keep the output constant. It's not very efficient, but it's simple and inexpensive.

    A DC to DC converter chops the input DC into AC, runs the AC through a transformer to step up/step down the voltage, and converts back to DC. They can be amazingly efficient (efficiency here is what percentage of input power is converted to output power, the remainder is lost to heat). DC-DC can be as efficient as 94% or so, shunt regulators are often less than 50%, although that depends a lot on the difference between the input and output voltages. If you could get a .5V shunt regulator (you can't, I've never seen one which worked below around 1.2V output). It would be very hard, but not impossible, to build a DC-DC regulator with a .7V output. Not sure how you can get below the "diode drop" voltage. All regulators consume energy when connected, so yes, you would need to switch them off when they weren't being used.
     
  2. mtwieg2

    mtwieg2 DE Bracket

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    I was thinking of using a simple current source regulator like a LM134 for each circuit under test. When the circuit is open, it draws zero current (though you would want some op amps to amplify the sense voltage). Only difficult part would be designing your connectors to contact each pin/socket in two locations for kelvin sensing.
     
  3. brtech

    brtech Podium

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    Go ahead and try it (I have). Like all real circuits, it's actually pretty hard to fix a bunch of production variables. You want 3 separate current source, but can you tolerate common grounds for those current sources? I think not, at least if you want to detect shorts. Can you run the op amps with a single supply? How tight is the gain specified on those op amps, and do you need a trimmer to adjust? What regulation are you asking of your power source for those op amps? Is that actually a better solution than a current meter with a voltage source and a trimmer to zero out current meter resistance variation along with a zero adjust that handles both voltage variation from a single C cell and contact resistance?
     
  4. Angelo Tringali

    Angelo Tringali Rookie

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  5. posineg

    posineg DE Bracket

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  6. ktinoue3

    ktinoue3 Podium

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    I like the form factor. How do you test two prong cords? This looks like it is more aimed at fencers than armorers?
     
  7. dcchew

    dcchew Podium

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    Very nice. What is the sampling rate for the microprocessor? A typical digital multimeter has a sampling rate of about 2.5 times per second which is too slow to catch intermittent breaks.
     
  8. ktinoue3

    ktinoue3 Podium

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    There are a bunch of videos on the page. It looks like it is pretty sensitive.
     
  9. dcchew

    dcchew Podium

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    Is this test box design able to detect intermittent breaks in a similar way that the Favero testers do? Looks fast doesn’t really mean much.
     
  10. ktinoue3

    ktinoue3 Podium

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    We will see what they say. This is the video I was referring too though.
     
  11. neevel

    neevel Armorer

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    Assuming the display refresh rate is fast enough to show short breaks, that is an ideal size to carry around for doing strip calls. Ron Herman used to have a small form-factor Textronix digital meter (with autoranging and a pseudo-analog bar so it could catch fast breaks), and small 6-postion switchbox with that he made to plug directly onto the face of the meter- the setup was similarly great for strip calls due to its size.
     
  12. Angelo Tringali

    Angelo Tringali Rookie

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    The instrument is home made
    The analog-to-digital conversion is 16 bits. The reading frequency is:
    10 cycles per second for the body wire,
    16 cycles per second for the weapon.
     
  13. Angelo Tringali

    Angelo Tringali Rookie

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    Not only the micro-interruptions are detected, but also the fast resistance variations between 10 ohms and infinity
     
  14. dcchew

    dcchew Podium

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    Nicely done! If you ever decide to sell your test box, you'd have plenty of buyers ready to stand in line.
     
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  15. Angelo Tringali

    Angelo Tringali Rookie

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    Thank you.
     
  16. brtech

    brtech Podium

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    Angelo, what method are you using to measure resistance? Current Source? Resistive divider?
    Since the machine is sensitive to contact on the order of 10-15 ms, I think 16 cycles per second (~60 ms) is too low. I would suggest that it needs to be on the order of 200 cycles per second. 10 is probably fine for body wires.
     
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  17. Angelo Tringali

    Angelo Tringali Rookie

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    I like your observation. I will work to perfect it. But you must consider that it is a small handmade instrument
     
  18. Angelo Tringali

    Angelo Tringali Rookie

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    Now the instrument makes a measurement every 15 ms. The frequency is about 70 Hz. By optimizing the code I could get higher frequency values. But I am sure that a good Armorer with this tool finds every problem on the tip of a weapon. For the moment I'm happy. For greater accuracy there is the Favero A2 tester.
     
  19. dcchew

    dcchew Podium

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    Any idea what the frequency rate is for the Favero A2? Just curious..
     
  20. Angelo Tringali

    Angelo Tringali Rookie

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