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Difference between 2-wire and 4-wire rtd
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jsummerfield
Electrical
Three and four wire RTDs permit compensation for the cable resistance in long distance measurements.
John
John
electricpete
Electrical
Correct. 4-wire rtd enables a 4-wire resistance measurement. One pair of leads is the current/source leads, the other pair of leads are the voltage/sensing leads.
Power (voltage or current) is applied at the current/source leads which run to the 2 terminals of the rtd. The only quantity measured in this set of leads is the current. There is a voltage drop in these leads due to high (relatively) current flow but it is irrelevant since we do not measure voltage on these leads, only current.
The voltage/sensing leads run independently and connect to the same two terminals at the rtd to sense to voltage there. At the instrument there is a high-impedance volt measuring device which ensures virtally no current flow. Therefore no lead voltage drop and an accurate current measurement.
Resistance is calcualted as voltage (from volt/sensing leads) divided by current (from current/source leads).
This same principle is used in many instruments other than rtd.
3-wire rtd runs doulbe lead to one terminal of the rtd and signle lead to the other terminal. Lead voltage drop is estimated based on comparing the two leads in the double pair.
Power (voltage or current) is applied at the current/source leads which run to the 2 terminals of the rtd. The only quantity measured in this set of leads is the current. There is a voltage drop in these leads due to high (relatively) current flow but it is irrelevant since we do not measure voltage on these leads, only current.
The voltage/sensing leads run independently and connect to the same two terminals at the rtd to sense to voltage there. At the instrument there is a high-impedance volt measuring device which ensures virtally no current flow. Therefore no lead voltage drop and an accurate current measurement.
Resistance is calcualted as voltage (from volt/sensing leads) divided by current (from current/source leads).
This same principle is used in many instruments other than rtd.
3-wire rtd runs doulbe lead to one terminal of the rtd and signle lead to the other terminal. Lead voltage drop is estimated based on comparing the two leads in the double pair.
jbartos
Electrical
- Jan 15, 2000
- 6,440
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2-wire versus 4-wire RTD applications can somewhat be related to temperature transmitters. If the transmitter can be located close to RTD, then the 4-wire RTD is not that much necessary.
etc. for more info
2-wire versus 4-wire RTD applications can somewhat be related to temperature transmitters. If the transmitter can be located close to RTD, then the 4-wire RTD is not that much necessary.
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