GFK-0467K Chapter 4 Series 90-30/20/Micro Instructions Set 4-17
4
OFDT The off-delay timer (OFDT) increments while power flow is off, and resets to zero when power
flow is on. Time may be counted in tenths of a second (the default selection), hundredths of a
second, or thousandths of a second. The range is 0 to +32,767 time units. The state of this timer is
retentive on power failure; no automatic initialization occurs at power-up.
When the OFDT first receives power flow, it passes power to the right, and the current value (CV)
is set to zero. (The OFDT uses word 1 [register] as its CV storage location—see the “Parameters:”
section on the next page for additional information.) The output remains on as long as the function
receives power flow. If the function stops receiving power flow from the left, it continues to pass
power to the right, and the timer starts accumulating time in the current value.
Note
If multiple occurrences of the same timer with the same reference address are
enabled during a CPU sweep, the current values of the timers will be the same.
The OFDT does not pass power flow if the preset value is zero or negative.
Each time the function is invoked with the enabling logic set to OFF, the current value is updated to
reflect the elapsed time since the timer was turned off. When the current value (CV) is equal to the
preset value (PV), the function stops passing power flow to the right. When that occurs, the timer
stops accumulating time—see Part C below.
When the function receives power flow again, the current value resets to zero.
ENABLE
Q
a42932
A
B
C
D
E
F
G
H
A= ENABLE and Q both go high ; timer is reset (CV = 0).
B= ENABLE goes low; timer starts accumulating time.
C= CV reaches PV; Q goes low, and timer stops accumulating time.
D= ENABLE goes high; timer is reset (CV = 0).
E= ENABLE goes low; timer starts accumulating time.
F= ENABLE goes high; timer is reset (CV = 0).
G= ENABLE goes low; timer begins accumulating time.
H= CV reaches PV; Q goes low, and timer stops accumulating time.