Rtd Sensor Connections - GE 469 Instruction Manual

3.2.9

RTD Sensor Connections

Note
3–20
If a voltage output is required, a burden resistor must be connected at the input of the
SCADA measuring device. Ignoring the input impedance of the input, R
For 0 to 1 mA, for example, if 5 V full scale is required to correspond to 1 mA, R
0.001 A = 5000 Ω. For 4 to 20 mA, this resistor would be R
Description
The 469 monitors up to 12 RTD inputs for Stator, Bearing, Ambient, or Other temperature
monitoring. The type of each RTD is field programmable as 100 Ω Platinum (DIN 43760),
100 Ω Nickel, 120 Ω Nickel, or 10 Ω Copper. RTDs must be three wire type. Every two RTDs
shares a common return.
The RTD circuitry compensates for lead resistance, provided that each of the three leads is
the same length. Lead resistance should not exceed 25 Ω per lead for platinum/nickel
RTDs or 3 Ω per lead for copper RTDs. Shielded cable should be used to prevent noise
pickup in the industrial environment. RTD cables should be kept close to grounded metal
casings and away from areas of high electromagnetic or radio interference. RTD leads
should not be run adjacent to or in the same conduit as high current carrying wires.
IMPORTANT: The RTD circuitry is isolated as a group with the Analog Input circuitry and
the Analog Output circuitry. Only one ground reference should be used for the three
circuits. Transorbs limit this isolation to ±36 V with respect to the 469 safety ground.
Reduced RTD Lead Number Application
The 469 requires three leads to be brought back from each RTD: Hot, Return and
Compensation. This can be quite expensive. It is however possible to reduce the number of
leads required to 3 for the first RTD and 1 for each successive RTD. Refer to the figure
below for wiring configuration for this application.
load
FIGURE 3–22: RTD Wiring
469 MOTOR MANAGEMENT RELAY – INSTRUCTION MANUAL
CHAPTER 3: INSTALLATION
= V / I
load full scale max
= 5 V /
load
= 5 V / 0.020 A = 250 Ω.
.