Hold Up Time

Hold up time is part of each configuration. It represents the time (in milliseconds) that device outputs are maintained in their current states after a communication disruption before reverting to their fallback values.

Hold up time settings can range from 50...65530 ms. By default, Control Expert sets hold-up time to 4 times the MAST Watch Dog setting. Because the default watchdog setting is 250 ms, Control Expert applies a default drop hold up time setting of 1000 ms.

Setting Hold Up Time for RIO Drops

When configuring MAST Hold up time , consider both of the following:

  • The maximum time between CPU requests.

  • MAST task watchdog time.

If Hold up time is not set to a sufficiently large value, the outputs of a drop may enter fallback during a switchover. This can cause a disruption in the behavior of outputs that have a fallback setting other than hold last value.

To accommodate both MAST and FAST tasks for (e)X80 RIO drops, Schneider Electric recommends setting drop Hold up time to a value not less than 4.4 times the MAST period.

M580 Hot Standby supports the following tasks:

Task

Type

Period

Watchdog time

Remote I/O platform:

Quantum RIO

M580 (e)X80

MAST1

Periodic

1...255 ms

10...1500 ms2

X

X

FAST

Periodic

1...255 ms

10...500 ms2

–

X

SAFE

Periodic

10...255 ms

10...500 ms2

–

X

X: Supported

–: Not supported

1. MAST task is mandatory and cannot be deactivated for both (e)X80 and Quantum RIO drops.

2. If CCOTF is activated, the minimum watchdog value is 64 ms.

Setting Hold Up Time for Distributed Equipment

The hold up time represents the time that device outputs are maintained in their current states after a communication disruption and before taking their fallback values. Because distributed devices are not connected to the primary CPU during a switch-over, set the hold up time to a value greater than the expected duration of the communication interruption.

For Modbus TCP devices:

  • Set the hold up time to exceed: 4.4 x (MAST period) + 600 ms.

For EtherNet/IP devices:

  • Set the hold up time to exceed: 4.4 x (MAST period) + 5000 ms.