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RTD & RESISTANCE CONNECTION
With the appropriate jumper settings, RTD and resistance measurements allow 2, 3 or 4-wire
RTD hookup to the J5 connector, as illustrated. The meter applies a fixed excitation current.
In 4-wire hookup,
the excitation and sense
wires are joined at the load. Resistance of
the excitation leads is not a factor, since ex-
citation is a constant current. Resistance of
the sense leads is not a factor, since voltage
sensing is at high impedance. 4-wire hookup
is recommended for long RTD cable runs
and for the R0 0-2 ohm and R1 0-20 ohm
ranges.
In 3-wire hookup,
the meter automatically
compensates for lead resistance by mea-
suring the voltage drop on only one current-
carrying excitation lead and multiplying that
drop by 2. Jumper
g
needs to be installed at
E2. The two leads need to have the same
resistance.
In 2-wire hookup,
the excitation and sens-
ing wires are joined at the meter to simplify
wiring to the load. Setup software described
below can measure the resistance of the
lead wires when these are shorted at the
load, and the meter then automatically sub-
tracts wire resistance from the resistance
measurement. The short should be as close as possible to the load. Ambient temperature
changes will still cause some error in the readings -- the higher the lead resistance, the greater
the error. OK to use 2-wire hookup without the special setup software steps below if wire
resistance is negligible compared to the resistance to be measured.
To eliminate lead wire resistance with 2-wire hookup, follow this procedure:
1.
Set the InPut menu item and jumpers for the desired range.
2.
Set SEtuP to
00_0
1
to set Control Input 2 (Pin P1-
4 on page 6) to “Peak or Valley.”
3.
Set ConFG to
000
11
(2-wire short).
4.
Short the two leads at the sensor end to create a 2-wire short.
5.
With the leads shorted at the sensor end, momentarily short Control Input 2 to Control Input
Return (Pin P1-4 to Pin P1-6 on page 6). This will store a value proportional to lead resist-
ance, automatically change COnFG to
000
10
(2-wire read), and Reset the meter.
6.
Remove the short and connect the sensor. The meter will now display sensor resistance less
wire resistance. You can now also change SEtuP.
If the range and associated jumpers are subsequently changed, the above procedure must be
repeated. This procedure is also available through Instrument Setup software.
