Using Alarm Relay and Set-points for Process Control
Our four-wire analyzers such as the 1056 and the 56 (with option -02 or -03) has 4 alarm relays which are useful for process control. The most basic set-up is to key in set-points in the analyzer which triggers the alarms, and in effect activate or de-activate an external device, like a pump or valve.
Available logics for set-point configured alarm relays are LOW and HIGH. If set to LOW, the alarm relay is triggered if the measured value is lower than the set-point. If set to HIGH, it is triggered if the measured value is higher than the set-point. This works well when the intention is to control based on a single set point.
Using relays to control a process that needs to be BETWEEN two set-points (range)?
By connecting relays with jumper wires you can combine their logic. To illustrate, here are some examples from actual customers:
Example 1: 1056 contacting conductivity analyzer, a single alarm is needed for <600uS/cm or >2000uS/cm. The alarm only goes to the DCS.
Solution: Combine 2 alarm relays on the 1056 as shown below and wiring the Normally Open and Common points on the relays:
- Alarm relay 1 is logic LOW, 600uS/cm
- Alarm relay 2 is logic HIGH, 2000uS/cm
By using jumper wires to connect the relays as shown, the DCS is alerted if either of the 2 alarms are triggered. This set-up will send the alarm to the DCS whenever the reading is below 600uS/cm OR above 2000uS/cm.
Example 2: 1056 pH analyzer needs to turn on a pump only if the pH is between 8 and 10. Outside of this range, the pump must be off.
Solution: This is done by combining 2 alarm relays on the 1056 and using the Normally Closed and Common Points for wiring:
- Alarm relay 1 is logic LOW, 8pH
- Alarm relay 2 is logic HIGH, 10pH
This set-up will keep the pump turned on within pH range of 8-10. Outside of this range, the alarm is triggered and the pump turns off.
I hope this discussion has been helpful in optimizing your Analytical instrument.