Vibro-Meter ABE044 – 6U 19-inch rack (with expansion slots)

ABE044 – 6U 19-inch rack (with expansion slots)

Channel inhibit function

The channel inhibit function allows individual AMC8 channels to be temporarily bypassed,

that is, it temporarily inhibits the protection offered by any associated relays.

The channel inhibit function is intended to allow a component in a measurement system

front-end, such as a sensor/transducer or signal conditioner, to be replaced for an individual

channel while the other machinery monitoring channels and functions continue to operate as

normal.

This allows the machinery being monitored to continue to operate (if the protection offered by

the other machinery monitoring channels and functions is adequate). It also allows any

control system using the relays to avoid false trips during such maintenance activity.

When the channel inhibit function is activated for an AMC8 channel:

• The channel continues its processing as per its configuration but inhibits the protection

offered by any associated relays.

This allows the effect of any changes to the measurement system front-end to be

observed. In this way, it can also be ensured that there are no ongoing alarm conditions

before the de-activation of the channel inhibit.

• Any DCoutput functionality associated with the channel continues, if enabled.

• The following flags (bits) for the channel processing are forced to a known state:

• The error bit (Err), OK system check (SOK), alarm (A+, A−) and danger (D+, D−)

flags are all forced to a normal state (which is false, that is =0).

The sensor bypassed (SBP) flag and the global channel OK fail flags are also set

active.

NOTE: The VM600 MPS1 and VM600 MPS2 software packages use the SBP (sensor

bypassed) flag to refer to the channel inhibit function.

• Any processing channels that depend on the channel are automatically bypassed.

• The channel’s status indicator (LED) on the panel of the AMC8 card slowly blinks green

for the duration of the channel inhibit (approximately once per second).

When the channel inhibit function is de-activated for an AMC8 channel, the card:

• Waits 12seconds for signal stabilisation (total recovery time).

• Resets (clears) any latched alarms.

• Stops forcing the flags for the channel processing to a normal state, so that the true

status of the machinery monitoring system is returned again. The sensor bypassed

(SBP) flag is also set inactive

1OK system checking

The OK System monitors the input signal from the sensor in order to verify if the sensor is

connected and operating normally. To do this, the DC signal level is compared against two

user-configurable OK levels: a minimum normal level and a maximum normal level.

Any problem with the transducer and/or signal conditioner or connecting cable that causes

the signal to deviate beyond these OK levels will cause an individual alarm for the input

channel (corresponding to the individual GlobalChannelOK bit).

As shown in Figure5-5:

• The “confirmation time” is a fixed firmware time delay used so that only an input signal

that is outside the configured OK levels for a time period greater than 250 ms is detected

as an OK system failure. This is used to ensure that noise (“spikes”) on the DC signal

level are not accidentally recognised as failures.

• The “response time” is the maximum time delay from the time that an OK system failure

is detected until the corresponding alarms are set (GlobalChannelOK bit for the input

channel). The actual time delay depends on the processor load of the card but is less

than 100ms.