GE Understanding ONDTR: Retentive On-Delay Timer Explained

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ONDTR

A retentive on-delay timer (ONDTR) increments while it receives power flow and holds its value when power flow stops. 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 ONDTR first receives power flow, it starts accumulating time (current value). When this timer is encountered in the ladder logic, its current value is updated.

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.

When the current value equals or exceeds the preset value PV, output Q is energized. As long as the timer continues to receive power flow, it continues accumulating until the maximum value is reached. Once the maximum value is reached, it is retained and output Q remains energized regardless of the state of the enable input.

a42931

ENABLE

RESET

Q

AB C D EF G H

A= ENABLE goes high; timer starts accumulating.

B= CV reaches PV; Q goes high.

C= RESET goes high; Q goes low, accumulated time is reset.

D= RESET goes low; timer then starts accumulating again.

E= ENABLE goes low; timer stops accumulating. Accumulated time stays the same.

F= ENABLE goes high again; timer continues accumulating time.

G= CV becomes equal to PV; Q goes high. Timer continues to accumulate time until ENABLE goes low, RESET goes high, or CV becomes equal to the maximum time.

H= ENABLE goes low; timer stops accumulating time.

When power flow to the timer stops, the current value stops incrementing and is retained. Output Q, if energized, will remain energized. When the function receives power flow again, the current value again increments, beginning at the retained value. When reset R receives power flow, the current value is set back to zero and output Q is de-energized. On 350 and 360 series PLCs, if the enable to the ONDTR is low, PV = 0 and reset R receives power-flow, then the output will be low. However, on the 311–341 PLCs, under these same conditions, the output will be high.

GFK-0467K Chapter 4 Series 90-30/20/Micro Instructions Set 4-11