How to check continuity/resistance

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  #1  
Old 11-01-05, 11:16 AM
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How to check continuity/resistance

Im trying to check the resistance of some thermistor components on my heating system and I am using a cheap analog multitester. I cannot get the needle to move on RX1 or RX50 and it only moves imperceptibly on the RX100 setting. The manufactuer of these thermistors shows a resistance range that is clearly way past the slight movement of the needle that I am getting. What am I doing wrong? Do I need a more sensitive ohm tester?
 
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  #2  
Old 11-01-05, 11:37 AM
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Try touching the test leads directly together. In any range, the pointer should move to '0' ohms. If not, there should be a 'zero adjust' control that you can use to make the meter point to '0'.

If you cannot get the meter to read '0' with the leads touching, then something is broken with the meter. This may be a broken lead, or a dead battery, or a dead meter.

An analog meter will require a battery for resistance measurements even if it works fine for voltage measurements.

You don't need a more sensitive meter for this application; simply one that works at all.

-Jon
 
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Old 11-01-05, 11:42 AM
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Yep I have done that; crossed the leads and zeroed the meter as best as possible. I also tried testing resistance on a simple object like a metal screw, and I got a good reading. I know these components work because they are new. (I am trying to read the resistance of these thermistors so I can calibrate a temperature setting). I guess I am wondering if its possible that certain types of thermistors can only be tested with a more sensitive multitester? For some reason it wont budge using this cheap one.
 
  #4  
Old 11-01-05, 12:00 PM
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What is the resistance range of the thermistors? It sounds like you need a different meter.

-Jon
 
  #5  
Old 11-01-05, 12:07 PM
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Well for the outdoor temp sensor resistance is 0-80, for the boiler temp sensor resistance is 0-14 and for the indoor temp sensor resistance is 8-22.
 
  #6  
Old 11-01-05, 05:52 PM
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You should get a reading somewhere in the scale on the Rx1 scale. On Rx50 or Rx100 you should be reading near zero ohms ( full scale on the meter.)

Not knowing about your devices, if they for some reason incorporate a diode then the polarity of the meter leads would matter. Try measuring with the leads reversed.
 
  #7  
Old 11-02-05, 07:27 AM
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yes, I have tried reversing the leads as well. Still no go. The devices are each connected to a thermostat wire that is not exactly short so I wonder if the length of the wire run is impeding the already low strength of the 1.5v battery.
 
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