As mentioned in previous Tech-Tips, the Advanced Relay Mode offers multiple boolean logic operators that can be used to trigger one relay based on 1, 2, or 3 relay sources. This feature Tech-Tip will provide an example of the
( a & b & c ) operator. In this example, a key point to demonstrate is that not all of the relay sources have to be used. Any combination of the two relay sources can be used. For example ( a & c ) or ( b & c ). This combination is valid for any of the advanced relay modes.
Consider the hypothetical Reverse Osmosis (RO) application below:
Assumptions:
1) The normal flow rate of the feed water is at least 25 GPM.
2) The normal pressure at the input of the RO membrane is 60 psi.
3) The flow sensor is upstream and at a substantial distance away from the pressure sensor.
4) The leak is between the flow sensor and the pressure sensor.
Logic
If the flow rate of the feed water is greater than or equal to 25 GPM
AND
if the pressure at the input of the Reverse Osmosis membrane is less than 60 psi
then
trigger an audio alarm to notify personnel of a leak after the flow sensor and before the pressure sensor.
This application may seem impractical, however, the goal of this Tech-tip is to provide an example of the advanced relay functionality.
Parameter Setup in the 8900 Multi-Parameter Controller
Relay 1 Source:
Multiple
Relay 1 Mode:
Advanced
Relay 1 Operator:
( a & b & c )
a = None, b = Relay 1 Source 2, c = Relay 1 Source 3
Relay 1 Source1:
None
Not used.
Relay 1 Source2:
Flow F1
Parameter to monitor the flow of the feed water to the RO system.
(b)
Relay 1 Mode 2:
High
Relay 1 Setpnt2:
25.000 GPM
Relay 1 Hys 2:
1.0000 GPM
Relay 1 Source3:
Pressure P2
Parameter to monitor the pressure at the input of the RO membrane.
(c)
Relay 1 Mode 3:
Low
Relay 1 Setpnt3:
55.00 psi
Relay 1 Hys 3:
0.000 psi
Relay 1 Delay:
0.0000 sec
Notice how only sources b and c are being used.
The "&" symbol refers to AND logic. If the condition for source "b" is true AND if the condition for source "c" is true, then trigger the relay.
