Document reference MAMPS-HW/E HARDWARE MANUAL
Edition 18 - March 2022 VM600 machinery protection system (MPS)
5-11
System self-checks
AMC8 / IOC8T CARD PAIR
5.9 System self-checks
5.9.1 OK 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. This is
shown in Figure 5-5.
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 Global Channel OK bit).
As shown in Figure 5-5:
• 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 (Global Channel OK bit for the input
channel). The actual time delay depends on the processor load of the card but is less
than 100 ms.
NOTE: The behaviour of the OK system checking is the same above and below the
configured OK levels.
Voltage sensor connection short-circuit or
current sensor connection open-circuit
Time
Time
Voltage sensor connection open-circuit or
current sensor connection short-circuit
Confirmation
time
100 msΔt < 250 ms
Response
time
100 ms
Recovery time
Figure 5-5: Maximum and minimum signal levels allowed by the OK System
Sensor OK
DC signal
level
Channel
OK
Grounded
Open
Min.
(Lower OK Level)
Max.
(Upper OK Level)
Normal
tolerance
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