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Old 7th Dec 2015, 1:58 pm   #1
Fourlegsgood
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Default Precautions to protect a CT160 meter during transit?

I have sold my AVO CT160 and need to send it by courier to the buyer. Is there a switch position or shorting out of terminals to protect the meter from damage during transit?

Thanks, Nick
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Old 7th Dec 2015, 2:22 pm   #2
John_BS
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Default Re: Precautions to protect a CT160 meter during transit?

I'm not aware of any damping precaution available other than adding a tantalum capacitor across the meter as part of the electrical protection regime. (See other posts).

I had a CT160 sent to me from Italy: it survived the trip to the UK, but was damaged on the return journey. The problem in that case was presumably a hard drop which caused the bakelite case of the meter to crack: this is a weak point if the meter retaining screws are over-tightened, over-stressing the meter casing. The actual movement survived! You could try packing the clam case internally with something like air-bags to apply distributed pressure to the front of the meter when the lid is closed.

John
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Old 7th Dec 2015, 2:32 pm   #3
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Default Re: Precautions to protect a CT160 meter during transit?

Thanks, it's all packed up now and with loads and loads of thick soft stuff between the metal clam and the box it is packed in. So I think any dropping will be well cushioned.

Pretty sure it will be OK. Just wanted to check for other ideas.
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Old 7th Dec 2015, 3:21 pm   #4
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Arrow Re: Precautions to protect a CT160 meter during transit?

The usual method for protecting any moving-coil meter from mechanical shock during movement is to simply strap the meter's terminals together with a piece of wire. Doing that damps the moving coil and thus reduces the force when the pointer hits the end stops. Often, the damping is sufficient to prevent the pointer from even reaching the far end stop. All of my m.c. meters that I have in store are protected that way.

Al.
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Old 7th Dec 2015, 5:24 pm   #5
GMB
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Default Re: Precautions to protect a CT160 meter during transit?

Quote:
adding a tantalum capacitor across the meter as part of the electrical protection regime.
Won't that result in wrong readings, given it works using a/c?
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Old 12th Dec 2015, 9:33 am   #6
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Default Re: Precautions to protect a CT160 meter during transit?

Quote:
Won't that result in wrong readings, given it works using a/c?
It's a DC meter, so the reading is the DC component of a rather spikey "mixed" waveform.

John
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Old 12th Dec 2015, 11:28 am   #7
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Default Re: Precautions to protect a CT160 meter during transit?

I haven't tested this, but by looking at the schematic the best you can do is to set the tester to Diode testing (D/R) with 1mA selected and select D1 or D2 and then short D1 and D2 to Cathode.

This ensures that the meter is shorted with the lowest possible internal resistance and that both ends are connected to the common Cathode. The meter is then shorted with approximately 2700 Ohm.

Shorting D1 and/or D2 to cathode can be done with the Terminal socket using top-cap leads or by selecting D1, D2 and Cathode for pin 1,2 and 3 on the roller selector and then making a short in any of the tube sockets, or in the flying lead socket for pin 1,2 and 3.

I couldn't find any other position of the switches with a lower internal resistance across the meter.

/Martin
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Old 12th Dec 2015, 11:26 pm   #8
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Default Re: Precautions to protect a CT160 meter during transit?

Martin.

Thank you. That was the sort of information I was hoping for. Unfortunately I had to ship it a few days ago. There have been no howls of dismay about a dead meter so I think it was ok. Hopefully your advice will be seen by any others shipping a CT160.
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