Xylem FC220 Data Logger Option - Manual (Page 8)

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8
V. Determining Relay States
The changing states of the relays are recorded as an analog voltage, generally on
channel 2. The voltage represents the state the relay was changed to at that time;
according to the equation:
Voltage in Volts = (50 + 50*S1 + 150*S2 + 450*S3 + 1350*S4) / 1000
Where S1 is the state of Relay1, S2 for Relay 2 ...
Off State, S = 0
On State, S = 1
Pulse State, S = 2
Thus a voltage between 0.050 and 4.050 Volts represents the states of all 4 relays.
The 4 relays have 81 possible combinations of states. The voltage is first
converted to an integer from 0-80 using this equation:
StateValue = INTEGER ((Voltage + 0.025) / 0.05) – 1
In base 3 this number 0-80 is in the range of 0000 to 2222. The most significant
digit is the state of relay 4, the least is the state of relay 1;
0 = Off
1 = On
2 = Pulse
These states are separated using these equations:
Relay 1 State = MODULUS (StateValue / 3)
Relay 2 State = MODULUS ( INTEGER (StateValue / 3), 3)
Relay 3 State = MODULUS ( INTEGER (StateValue / 9), 3)
Relay 4 State = INTEGER (StateValue / 27)