5 Function blocks
5.1 A, analog value comparator/threshold value switch
138
Control Relay easy800
11/11 MN04902001Z-EN
www.eaton.com
Function of the function block
The function block compares values present at the inputs I1 and I2. You
control the comparison in the function block by setting other input
parameters:
•
Multiplication factors F1 and F2 for the comparison values 1 and 2,
•
Offset of comparison value 1 via function block input OS,
•
Application of a switch hysteresis to comparison value 2 on HY.
Contact Q1 indicates the comparison result “greater”, “equal to” or “less”
depending on the set operating mode.
Contact CY closes if the value range is exceeded. If an out-of-range value is
signalled with CY = 1, Q1 remains in state 0. With the following formulae you
can calculate the permissible value range.
– 2
31
I1 F1 + OS (2
31
– 1) CY = 0
– 2
31
I2 F2 + HY (2
31
– 1) CY = 0
– 2
31
I2 F2 – HY (2
31
– 1) CY = 0
The following signal diagram illustrates the function:
Figure 103:Signal diagram for analog value comparator
1: actual value at I1
2: Setpoint value on I2
3: Hysteresis on HY
4: Switching contact Q1 (N/O contact)
5: Offset for value I1
6: Actual value plus offset
• Range A: Compare I1 greater than I2
– The actual value I1 increases.
– The contact switches when the actual reaches the setpoint value.
– The actual value changes and falls below the value of the setpoint value minus the hysteresis.
– The contact goes to the normal position.
• Range B: Compare I1 less than I2
– The actual value drops.
– The contact switches if the actual value reaches the setpoint value.
– The actual value changes and rises above the value of the setpoint value plus hysteresis.
– The contact goes to the normal position.
1
1
3
2
4
CY
A
B
D
3
6
1
5
C