Xylem CR500 CIRCULAR CHART RECORDERS - Manual (Page 10)

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Thermocouple (TC) Installation Guidelines
Proper sensor installation can eliminate many problems in a control system. The probe
should be placed so that it can detect any temperature change with minimal thermal lag.
In a process that requires fairly constant heat output, the probe should be placed close to
the heater. In a process where the heat demand is variable, the probe should be close to
the work area. Some experiments with probe location are often required to find this
optimum position.
Proper sensor type is also a very important factor to obtain precise measurements. The
sensor must have the correct temperature range to meet the process requirements. In
special processes, the sensor might need to have different requirements such as leak-
proof, anti-vibration,
Standard thermocouple sensor limits of error are 4° F (2° C) or 0.75% of sensed
temperature plus drift caused by improper protection or an over-temperature occurrence.
This error is far greater than controller error and cannot be corrected at the sensor except
by proper selection and replacement.
In order to connect the probe input device to the recorder, you must first gain access to
the PC board that is mounted to the back of the chart plate.
A ferrite bead has been included to provide additional protection for electrical “Noise”
sensor signal wires can pick up. See drawing below for correct installation of this device.
(Figure 2.3)
Ungrounded thermocouples recommended on 2 pen units.
Figure 2.3
CAUTION! DO NOT TOUCH the terminals of the transformer while the
recorder is connected to the main AC power supply. To avoid the risk of possible electric
shock, unplug or disconnect the recorder from the main power supply before attempting
to open the recorder. If the recorder is installed with the battery back-up option,
disconnect the 9 Volt battery to avoid damaging the recorder and draining the battery.
Your recorder will have a hinged chart plate held in place by two (2) screws located on
the right hand side of the chart plate. Remove these two screws and open the hinged chart