Noise
- Thread starter JdoubleU
- Start date
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zbang
Senior Member
- Location
- Roughly 5346 miles from Earls Court
What kind of sensor? (Thermistor? RTD? Thermocouple? etc)
How's it connected? (direct to receiver panel, 4-20ma, etc)
What type of wire? Shielded?
What's grounded where?
And, is noise the problem, anyway? How are they sure it's not a flaky sensor or receiver electronics?
How's it connected? (direct to receiver panel, 4-20ma, etc)
What type of wire? Shielded?
What's grounded where?
And, is noise the problem, anyway? How are they sure it's not a flaky sensor or receiver electronics?
I went over there and noticed that telecom had put a isolation transformer and they said it seems to have solved the problem. If there is a motor on this circuit would this load due to it inductive nature cause noise on the line? Could it also be that current is leaking to ground?
zbang
Senior Member
- Location
- Roughly 5346 miles from Earls Court
I'll make a WAG and say there's an unintended ground on the line somewhere. The transformer make the problem appear to go away, but of course doesn't actually fix anything.
When you say unintended ground somewhere are you thinking that the neutral could be touching ground somewhere in the circuit besides at the main.
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
100129-1224 EST
Jakewhis:
I am going to ignore the comments made so far.
You have a fundamental troubleshooting problem.
You described the device as a temperature sensor monitor.
(1) Does this control anything or just display a temperature reading?
(2) What kind of temperature sensor?
(3) Can it monitor more than one sensor?
(4) Is this AC or battery powered?
(5) Is the display digital or an electro-mechanical meter?
(6) Can you substitute a spare sensor for the one currently connected to the monitor?
(7) Is the sensor of a type that shorting the input leads at the monitor would produce a useful reading?
(8) What is the min and max temperature that can be read on the current setting of the monitor?
(9) What does flaky mean? (Display constantly jumps, or just a wrong reading.)
(10) How long is the cable from the sensor to the monitor?
(11) What information is there on how the cable is wired (shielded or not, chassis connected and/or grounding of shield), (transducer wiring - floating or one side connected to chassis), etc.
At least some of these items of information should have been in your original post. But whoever called you may have provided no information.
.
Jakewhis:
I am going to ignore the comments made so far.
You have a fundamental troubleshooting problem.
You described the device as a temperature sensor monitor.
(1) Does this control anything or just display a temperature reading?
(2) What kind of temperature sensor?
(3) Can it monitor more than one sensor?
(4) Is this AC or battery powered?
(5) Is the display digital or an electro-mechanical meter?
(6) Can you substitute a spare sensor for the one currently connected to the monitor?
(7) Is the sensor of a type that shorting the input leads at the monitor would produce a useful reading?
(8) What is the min and max temperature that can be read on the current setting of the monitor?
(9) What does flaky mean? (Display constantly jumps, or just a wrong reading.)
(10) How long is the cable from the sensor to the monitor?
(11) What information is there on how the cable is wired (shielded or not, chassis connected and/or grounding of shield), (transducer wiring - floating or one side connected to chassis), etc.
At least some of these items of information should have been in your original post. But whoever called you may have provided no information.
.
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
100129-1325 EST
Jakewhis:
Suppose this is a thermocouple sensor. Disconnect the sensor cable from the display instrument. Connect a meter, such as a Fluke 27, to the sensor leads. A J type (iron-constantan) produces about 55 microvolts/C relative to the ambient temperature of your meter lead terminations to the thermocouple leads. If you get a steady reading and the temperature of the sensor is constant, then it may not be a sensor problem. But does not exclude noise added to the signal when the sensor is connected to the the monitor.
Continuing with the same type of sensor connect a short at the monitor input and the input voltage is therefore 0. This is equivalent to the sensor and the instrument being at the same temperature. Thus, the instrument should read close to room temperature assuming there is a zero reference in the monitor. Reading should be stable.
If a thermistor sensor, then after disconnecting from monitor use your ohmmeter to measure resistance. Should be stable. If so put a fixed resistor of about the resistance of the sensor at the input of the monitor and see if the reading is stable.
Same for an RTD, but may be a lower resistance.
A Dallas 1-wire sensor would be much more difficult for you to evaluate.
http://en.wikipedia.org/wiki/Thermocouple
has typical voltage constants.
.
Jakewhis:
Suppose this is a thermocouple sensor. Disconnect the sensor cable from the display instrument. Connect a meter, such as a Fluke 27, to the sensor leads. A J type (iron-constantan) produces about 55 microvolts/C relative to the ambient temperature of your meter lead terminations to the thermocouple leads. If you get a steady reading and the temperature of the sensor is constant, then it may not be a sensor problem. But does not exclude noise added to the signal when the sensor is connected to the the monitor.
Continuing with the same type of sensor connect a short at the monitor input and the input voltage is therefore 0. This is equivalent to the sensor and the instrument being at the same temperature. Thus, the instrument should read close to room temperature assuming there is a zero reference in the monitor. Reading should be stable.
If a thermistor sensor, then after disconnecting from monitor use your ohmmeter to measure resistance. Should be stable. If so put a fixed resistor of about the resistance of the sensor at the input of the monitor and see if the reading is stable.
Same for an RTD, but may be a lower resistance.
A Dallas 1-wire sensor would be much more difficult for you to evaluate.
http://en.wikipedia.org/wiki/Thermocouple
has typical voltage constants.
.
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