Emerson Fisher FLOBOSS 407, Инструкция по эксплуатации

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FloBoss 407 Instruction Manual
3-26 Rev 5/00
I SRC
+
-
2-W IRE, 100 OHM
ROC-POW ERED
RTD PROBE
RED
W HT
B
W HT
C
W HT
RED
A
DOC4007A
Modified
RTD
Figure 3-22. RTD Input Module Field Wiring for Two-Wire RTDs
Three-wire RTDs have an active element loop and a compensation loop. The active element loop
is connected across terminals A and B. The compensation loop is connected across B and C. The
compensation loop helps increase the accuracy of the temperature measurement by allowing the
RTD module to compensate for the resistance of hookup wire used between the probe and RTD
module.
In operation, the RTD module subtracts the resistance between terminals B and C from the resistance
between terminals A and B. The remainder is the resistance of only the active element of the probe.
This compensation becomes more important as the resistance of the hookup wire increases with
distance between the probe and the ROC/FloBoss. Of course, in order to perform properly, the
compensation loop must use the same type, size, and length of hookup wire as the active element loop.
The RTD module is designed for only one compensation loop, and this loop is not isolated from the
active element loop because terminal B is common to both loops. In the 3-wire RTD, the wires are
connected to module terminals A, B, and C, as shown in Figure 3-23.
It is important to match the color coding of the RTD probe wires to the proper module terminal,
because the probe wire colors vary between manufacturers. To determine which leads are for the
compensation loop and which are for the active element, read the resistance across the probe wires with
an ohmmeter. The compensation loop reads 0 ohms, and the RTD element reads a resistance value
matching the temperature curve of the RTD.
3-WIRE,100-OHM,
RTD PROBE
WHT
WHT
RED
WHT
C
RED
WHT
B
A
DOC0161A
Modified
RTD
I SRC
Figure 3-23. RTD Input Module Field Wiring for Three-Wire RTDs