Measurement Computing LogBook Series - Manual (Page 170)

LV-44 LogView 989592 Software Reference
The Scan Rate block is the right half of the Acquisition Configuration window (see previous figure).
To set the scan rate, you can use LogBook’s “internal” clock, or an “external” clock. Brief descriptions
follow.
Note: The scan-to-scan time is not recorded when tracking variable-speed events.
• Internal Clock . The scan-to-scan timing may be set by a fixed-frequency pacer clock.
LogBook’s time-of-day clock has 1/16-second resolution for data-logging applications where
acquisitions must be performed at specific times during the day. The time of occurrence for each
acquisition and its trigger are recorded with the data. The internal clock can be reset in the
LogBook Monitor window in the Device menu.
• External Clock . Each scan may be individually started by an external TTL level trigger to
allow the scan rate to track an external, variable-speed event (such as engine revolutions). The
external clock signal is applied to LogBook through pin 20 of the P1 DB37 Analog I/O connector.
The P1 pinout is included in chapter 4.
Question: Why is the Pin 20 [for the external clock] identified as PCRCLK output/input?
Answer: When LogBook is set for an external user-supplied pacer, pin 20 has an input function.
When LogBook is set to make use of its internal FPGA (Frequency Pulse Gain Amplifier)
supplied pacer, pin 20 is driven as an output. This allows instrumentation external to LogBook to
be triggered in sync with LogBook scans.
Question: On what edge is the sample taken? Rising or Falling?
Answer: Rising edge, low-to-high direction, where the minimum pulse high-time equals the low
time (100nsec).
For applications with both slow and fast phenomena, sampling slow signals at a slower rate while
maintaining high rates for fast signals will conserve memory. For example, channel 1 may read fast signals
like vibration and can be sampled at the high (base) rate; channel 2 may read slow signals like
thermocouples and can be sampled at a lower rate. A Base Rate A and up to 3 more rates (B, C, D) can be
configured; but only one base rate can be defined for the entire system and it should be set for the fastest
scan required. The B, C, D rates must be integer (whole number) divisions of the base rate. It is also
possible to scan the same channel at several rates.
Note: A separately indexed data file is created for each scan rate.
The checkbox “Apply noise reduction averaging” refers to auto-averaging for scan rates B, C, and D.
All channels are scanned at the base rate; but they may also be scanned at divisions of the base rate. Two
advantages to averaging are noise reduction by limiting the effect of extraneous readings and storage
savings since fewer values are stored.
• Averaging. Checking this box, the readings from the base rate will be averaged, and the average
value will be entered for the derived rate scan. If the scan rate B is ¼ of the base rate A,
then four A readings will be averaged for each B reading.
• No averaging. Not checking this box, the readings at the derived scan rates will be exactly the same
for that time-point as the base rate.
Event Marking/Time Stamping
The top right side of the Acquisition Configuration window allows you to manually mark events and/or
insert an absolute time reference for each scan:
• Enable Event Mark sets up the acquisition for an operator to press the button in the
LogBook Monitor window or on the LBK1 remote operation terminal. Whenever the button is
pressed, that data point is added to the data file.
• Enable Time Stamp sets up the acquisition to automatically add the time (to ms) and date to the data
file for every scan.