Resistor Value Change

Hello all,

This is an electronic question, it is related to a security panel and the End Of Line Resistor. For those that do not know the EOLR is a resistor that in placed within the protected loop to provide a small amount of current to flow and thus supervises the loop. If the loop is cut it is an alarm, if the loop is shorted it could be an alarm or trouble depending upon the status of the panel. Enough background.

Today I had a strange occurrence with a EOLR. The system was not reporting the zone open even though I was holding the door open and looking at the keypad. After a period of troubleshooting found that the 3.74k resistor was now 5.86k. Replaced with new and all is well. This is the second time in 17 years that this has happened to me. Very Strange??? I wonder what would make it change in this way. Any thought???

Just looking for opinions on this. The environment was a clean office, normal temps, humidity very comfortable. No signs of overheating of the resistor, no corrosion present. All looked as it did when I installed about

4 years ago except for the very high value.

Thanks in advance.

Les

Reply to
ABLE_1
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Any idea who manufactured the original resistor? Could be a junk brand...

The only problem I have had was with 0.6W metal film resistors going high (Beyschlag now part of Vishay) when operating directly on 240Vac circuitry. Even an identical replacement failed some months later. They didn't seem to like it for some reason. After finally replacing with a high quality carbon film type it worked fine and never failed again.

I can't imagine that your resistor would be operating at 240Vac levels so I can't surmise what caused it to go high.

Reply to
Ross Herbert

If the door was open how did the panel see the resistor ? the resistor must of been before the door switch .because with the door open (door switch not made or shorted) the panel can not see the resistor . It is only(resistor) used for supervision.

Reply to
Bob

upon

was

17

when in doubt, blame lightning.

about

the quality of basic components seemes to be in a decline these days.

Reply to
TimPerry

"ABLE_1" bravely wrote to "All" (19 Feb 06 12:55:16) --- on the heady topic of "Resistor Value Change"

AB> From: "ABLE_1" AB> Xref: core-easynews sci.electronics.repair:358702

AB> Hello all,

AB> This is an electronic question, it is related to a security panel and AB> the End Of Line Resistor. For those that do not know the EOLR is a AB> resistor that in placed within the protected loop to provide a small AB> amount of current to flow and thus supervises the loop. If the loop AB> is cut it is an alarm, if the loop is shorted it could be an alarm or AB> trouble depending upon the status of the panel. Enough background.

AB> Today I had a strange occurrence with a EOLR. The system was not AB> reporting the zone open even though I was holding the door open and AB> looking at the keypad. After a period of troubleshooting found that the AB> 3.74k resistor was now 5.86k. Replaced with new and all is well. This AB> is the second time in 17 years that this has happened to me. Very AB> Strange??? I wonder what would make it change in this way. Any AB> thought??? AB> Just looking for opinions on this. The environment was a clean AB> office, normal temps, humidity very comfortable. No signs of AB> overheating of the resistor, no corrosion present. All looked as it AB> did when I installed about 4 years ago except for the very high value.

AB> Thanks in advance.

AB> Les

Perhaps the damage to the film resistor is due to static discharge by people walking up or from their clothes or a nearby copy machine. Try protecting the line with a small spark gap or, if the voltage is low, a small neon tube across that resistor.

A*s*i*m*o*v

... Integrated Circuit (n): a device used to protect fuses.

Reply to
Asimov

The resistor was in series with the door switch. As to the operation of the zone all is now well with the proper resistor so that is of lesser importance.

My main question is to what would cause a resistor to change value to this level with out any noticeable physical changes such as heat or something???

It does seem to be a strange question I know and maybe one that will never be answered. I was just looking for some opinions or ideas as to why.

Thanks

Reply to
ABLE_1

My 'stock' of resistors is based on 0.6w metal film types and I've never known this to happen.

--
*I don't know what your problem is, but I'll bet it's hard to pronounce 

    Dave Plowman        dave@davenoise.co.uk           London SW
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Reply to
Dave Plowman (News)

On Sun, 19 Feb 2006 12:55:16 -0500, "ABLE_1" put finger to keyboard and composed:

I had this same problem in several units of one particular monitor. In each case a 1/4W carbon resistor had gone high in value. Dissipation was not an issue as the resistor was operating well within its design limits, and the circuit had no other faults. The operating voltage was only 5V, ie TTL.

I've also experienced open resistors in resistor packs, again at TTL voltage levels.

- Franc Zabkar

--
Please remove one 'i' from my address when replying by email.
Reply to
Franc Zabkar

Franc,

So then the guess would be the resistor was bad to start and then when exposed to some current flow it just went HI??? That is a plausible answer then. Still very strange indeed. One just never knows some days.

Thanks for the input.

Les

Reply to
ABLE_1

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