The Inor SR535 Alarm Unit is built for monitoring Pt100 signals in the process industry. The unit gives alarm functions for either increasing or decreasing temperatures and for certain error states. SR535 provides an output signal, 4-20 mA, which is equivalent to the measurement range.
SR535 is equipped with one output relay, Re 1, with switch over contact for temperature monitoring.
A relay connected for normally active function, Re 2, gives a contact breaking function for sensor breakdowns, supply voltage failure, and measurements exceding 125% of the normal range. Re 2 should only be used to indicate that measurements (and monitoring) may not be correct.
An accurate 4-20 mA output signal is available. The signal is temperature linear and equivalent to the calibrated temperature range.
Configuration changes are made conveniently with jumpers. The following adjustments are available: temperature measuring range (see specifications), High/Low-alarm, the relays normally active or passive functions, alarm delay 0.4 or 2 s, hysteresis 0.5 or 5 %. A voltage outlet and a potentiometer on the front panel are used to adjust the set-point. The set-point can be measured as a voltage from the test outlet. The scale is 0-5 V for 0-100 % of input signal.
The relays "normally active or passive" functions are chosen to suit the use of the monitor. Normally active, with the relay coil activated and the monitor inactive (no alarm), is suitable when the monitor is used to give an alarm signal at error states . This means that in case of a power supply failure the monitor will give an alarm signal (=monitoring out of order). Normally passive is mostly used to provide a trip function to switch off equipment, thus saving costly and unnecessary operational stops. The choice of High or Low alarm functions depends on whether increasing or decreasing signal is to be monitored. Alarms are always indicated by a lighted red LED, independent of configuration. Open or closed relay contacts The choice of open or closed relay contacts is made when connecting the output signal lines.
Comparison of monitored input signals to the adjusted set-point is carried out in two stages using a special principle, which gives a very efficient filtering of transient interference and noise. Reliability in the monitoring system is increased with a dynamic hysteresis, which connects the preset hysteresis when an alarm is monitored. The relays in the SR535 will not give a false alarm when power is switched on. A 15-turn potentiometer insures high definition and stability in adjusted set-point. The hysteresis level can be changed with jumpers on the circuit board.
All connections are made with plug-in screw terminals. Installation is simplified by connection diagrams on the front panel. Compact mounting on DIN-rail SR535 snaps on to a 35 mm DIN-rail and can be mounted with high density.
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