4
CTI 2557-A Installation and Operation Guide
1.5
Effect of Out-of-Range Input Signals
RTD inputs exceeding 849.8 degrees C for 100 Ohm platinum or 260.0 degrees C for 120 Ohm nickel
and 10 Ohm copper will cause the overrange bit to be set. A maximum temperature of 849.9 degrees
C for 100 Ohm platinum or 260.1 degrees C for 120 Ohm nickel and 10 Ohm copper will be returned
for any positive overrange input.
Similarly an input below -199.8 degrees C for 100 Ohm platinum or -79.8 degrees C for 120 Ohm
nickel or -100 degrees C for 10 Ohm copper will cause the underrange bit to be set.
Figure 5 Effect of Voltage Input - 100 Ohm Platinum
Figure 6 Effect of Voltae Input - 120 Ohm Nickel
NOTE:
The Model 2557-A uses the least significant bit (16) to indicate an open RTD. The
value of this bit is set to 1 when this condition occurs.
