nVision
Operation Manual
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Page 25
2-,.3-,.or.4-Wire.Measurements
In order to measure temperature, the RTD sensing element must be connected through the
IP67 rated, M8 connector (P/N 3953) provided with your RTD100 module.
Since the temperature
measurement is based on the sensing element resistance, any other resistance in the system
(lead wire, connections, etc) may be added to the measurement circuit and will result in mea-
surement error.
Care must be taken to eliminate the effects of any unwanted resistance in order
ensure the best possible measurements.
The three wiring methods are:
2-wire:
3-wire:
4-wire:
In the 2-wire method, the sensor resistance measurement includes the lead wire resistance.
This
method is typically used only when lead wires are very short, or when high measurement ac-
curacy is not required.
In the 3-wire method, two lead wires connect to one side of the RTD sense element while the
third lead connects to the other side. The two adjoining lead wires cancel each other out allow-
ing the nVision to read the RTD sense element without the associated lead resistance measure-
ment error. This self canceling resistance value is also subtracted from the other leg with the
assumption that the two are equal.
Your nVision is also capable of 4-wire measurements.
The fourth wire allows the other side of
the lead wire to self cancel independently, thus reducing your measurement uncertainty to a
greater level.
It is also necessary to ensure that your nVision is properly configured in
CrystalControl to the proper RTD Lead Type present. You can validate your nVision setting in the
Summary menu item under the Settings button. The following matrix applies if your nVision
Lead Type setting and the actual wiring of your RTD sense element do not match.
RTD Sense Element Wired Into M8 Connector (PN/3953)
2-wire
3-wire
4-wire
CrystalControl
Lead Type
Setting
2-wire
Valid 2-wire data
Valid 2-wire data
Valid 2-wire data
3-wire
Invalid data
Valid 3-wire data
Valid 3-wire data
4-wire
Invalid data
Invalid data
Valid 4-wire data
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