COSA Xentaur Xentaur XDTL-HT - Manual (Page 29)

Relays
29
Relays
The XTDL-HT™ can control up to four relays. Relay 2 is reserved for controlling the enclosure heater.
Relays 3 & 4 require the optional I/O board. Each relay can be configured to activate by the following
conditions:
 Measurement alarm
 System event
 PID controller
 Time and day
 Modbus command
If a relay variable is assigned to a measurement, the relay will be activated when the measurement
value meets the relay alarm state which can be:
 Measurement value < low alarm threshold
 Measurement value > high alarm threshold
 Measurement value is outside of low and high alarm thresholds
 Measurement value > low alarm threshold
 Measurement value < high alarm threshold
 Measurement value is between low and high alarm thresholds
The instrument has a hysteresis built-in so that the relays would not continuously toggle when the
measurement value is close to the threshold value.
If a relay variable is set to an event or a PID controller, the alarm state indicates the relay polarity
which can be either normally-on or normally-off.
The relays can also be configured to operate on system fault even when they are set to operate on
measurement alarm or event. On the event of a system fault, a relay can be triggered as an alarm or it
can continuously toggle at a 2-sec interval. This function is useful for signaling the DCS system with two
events by using only one relay signal. For example, a relay can be configured to trigger when dew point
measurement goes out of range or when a system fault occurs.
Once a relay is activated by a measurement alarm or a system fault, it can stay activated or it can be
deactivated automatically when the condition clears. If the Self Cleared function is enabled, the relay
will deactivate itself when the instrument clears the triggering condition. Otherwise, user is required to
select the Reset Alarm menu item to reset the relays.