Campbell CR6 Series, Operator'S Manual

Page: 387 / 690

387
8. Operation
Related Topics:
• Quickstart
(p. 39)
• Specifications
(p. 101)
•
Installation
(p. 137)
• Operation
(p. 387)
8.1 Measurements — Details
Related Topics:
• Sensors — Quickstart
(p. 39)
•
Measurements — Overview
(p. 71)
•
Measurements — Details
(p. 387)
• Sensors — Lists
(p. 657)
Several features give the CR6 the flexibility to measure most sensor types. Some
sensors require precision excitation or a source of power. See Switched-Voltage
Output — Details
(p. 473).
8.1.1 Time Keeping — Details
Related Topics:
• Time Keeping — Overview
(p. 71)
•
Time Keeping — Details
(p. 387)
—Measurement of time is an essential function of the CR6. Time measurement
with the on-board clock enables the CR6 to attach time stamps to data, measure
the interval between events, and time the initiation of control functions.
8.1.1.1 Time Stamps
A measurement without an accurate time reference has little meaning. Data on
the CR6 are stored with time stamps. How closely a time stamp corresponds to
the actual time a measurement is taken depends on several factors.
The time stamp in common CRBasic programs matches the time at the beginning
of the current scan as measured by the real-time clock in the CR6. If a scan starts
at 15:00:00, data output during that scan will have a time stamp of 15:00:00
regardless of the length of the scan or when in the scan a measurement is made.
The possibility exists that a scan will run for some time before a measurement is
made. For instance, a scan may start at 15:00:00, execute time-consuming code,
then make a measurement at 15:00:00.51. The time stamp attached to the
measurement, if the CallTable() instruction is called from within the Scan() /
NextScan construct, will be 15:00:00 , resulting in a time-stamp skew of 510 ms.