Spectrum Controls 1756sc-IF8u User Manual

Page 57

Chapter 5:

Channel Configuration, Data, and Status

Rate Alarm

The rate alarm triggers if the rate of change between input samples for
each channel

exceeds the specified trigger point for that channel. It is

based on the channels .RangeType native units per second. (V, mA, degC

(.TempMode = 0), degF (.TempMode = 1), Ohms.)

For example, if you set the a channel, with a voltage range type, to a rate

alarm of 1.0 V/S, the rate alarm will only trigger if the difference between

measured input samples changes at a rate > 1.0 V/S. If the module’s

actual sampling time is 100 ms (i.e. sampling new input data every 100ms)

and at time 0, the module measures 5.0 volts and at time 100ms measures

5.08 V, the rate of change is (5.08V - 5.0V) / (100mS) = 0.8 V/S. The

rate alarm would not set as the change is less than the trigger point of

1.0V/s.

If the next sample taken is 4.9V, the rate of change is (4.9V-5.08V)/

(100mS)=-1.8V/S. The absolute value of this result is > 1.0V/S, so the rate

alarm will set. Absolute value is used because rate alarm checks for the

magnitude of the rate of change being beyond the trigger point, whether a

positive or negative excursion.

Note: The module acquires data continuously even though it is only

reported to the controller at the .RealTimeSample rate. The sampling time

used for calculating the rate alarm is the acquisition rate. This can be

determined by setting the .RealTimeSample tag to 10ms (Faster than the

module can acquire data) and record the difference between successive

.RollingTimeStamp values.

.AlarmEnable

0, 1

BOOL

0: Process and rate alarms are disabled

1: Process and rate alarms are enabled.

.ProcessAlarmLatch

0, 1

BOOL

0: Process alarms are not latched.

1: Process alarms are latched.

.RateAlarmLatch

0, 1

BOOL

0: Rate alarm is not latched.

1: Rate alarm is latched.

.RateAlarmLimit

0 to 4x of native signal value

REAL

Specifies a rate alarm will occur if the input data changes more than the

configured amount per second between two successive reads either

negative or positive. Specified in units (V, mA, Ohms, DegC, DegF) per

second.