Laurel-electronics LTM CTR SERIES PULSE, AC or PROCESS TOTALIZER INPU User Manual download pdf (Page 26)

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band is often used to minimize relay chatter. A wide hysteresis band can be used for on-off

control applications. The hysteresis band equals two hysteresis limits.

A deviation band controls relay action symmetrically around a setpoint. The relay actuates

when the reading falls within the deviation band, and de-actuates when the reading falls

outside. A limit (such as 50 counts) is set up around both sides of the setpoint to create the

deviation band, which equals two limits. Passbands around a setpoint are often used for

component testing.

14. INPUT SIGNAL FILTERING

A moving average filter is selectable in software to process the internal digital readings, which

are taken at 60/sec with 60 Hz power and 50/sec with 50 Hz power. Eight moving average

settings are selectable with the following equivalent RC time constants: 0.08 sec, 0.15 sec, 0.3

sec, 0.6 sec, 1.2 sec, 2.4 sec, 4.8 sec, 9.6 sec. The longer time constants provide superior

noise filtering at the expense of fast response time.

Adaptive moving average filtering allows the transmitter to respond rapidly to actual changes

in signal while filtering out normal noise. An adaptive filter threshold causes the moving

average filter to be reset to the latest reading when the accumulated difference between

individual readings and the filtered reading exceeds that threshold. The accumulated difference

is also reset to zero when the latest reading has a different polarity than the filtered reading. The

adaptive filter threshold can be selected as low or high. Low is normally selected. High should

be selected if the signal has large transients.

15. TRANSMITTER CALIBRATION

All ranges of transmitters have been digitally calibrated at the factory prior to shipment using

computers and calibration equipment certified to NIST standards. If recalibration is required, the

transmitter may be returned to the factory or to an authorized distributor.

The counter main board contains an EEPROM, which stores calibration constants for the quartz

crystal oscillator and the analog output. The V-to-F converter signal conditioner board stores its

own stores its own voltage-to-frequency calibration constants EEPROM. The dual channel pulse

input signal conditioner and quadrature signal conditioner boards do not require calibration. As a

result, transmitter boards can be interchanged without requiring recalibration.

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Laurel-electronics LTM CTR SERIES PULSE, AC or PROCESS TOTALIZER INPU User Manual Page 26