12
CTI 2557-A Installation and Operation Guide
2.6
Wiring the Input Connectors
RTD input signals are accepted through a 64 position fixed connector with wire press in terminals
located on the front of the module. Consult the RTD manufacturer's recommendations for selecting the
input wire type and size. The connector will accept 18 to 30 AWG wire.
The Model 2557-A uses a fixed connector to terminate field wiring. This is used because the chemistry
of a removable connector may have an adverse effect on the accuracy of the measurement. CTI has
carefully selected a connector that minimizes this effect.
Refer to Figure 13 for correct wiring for 2, 3, or 4 wire RTDs to the Model 2557-A. Each channel
consists of four press in terminals. Insert wire by using a small screw driver to depress the spring
tension lever and then insert the wire. Solid core wires may be pushed in without depressing lever.
Remove wire by depressing spring lever to remove tension and then remove lead wire. (See Figure 12)
The Model 2557-A may compensate for up to 20 Ohm of lead resistance per wire. Use the table in
Figure 9 in planning the maximum distance the RTD may be located from the module.
Figure 13 Copper Wire Table at 25 Degrees Celsius
