Section 8. Operation
472
synchronize measurements or other functions, using the
WaitDigTrig()
instructions, independent of CR6 clocks or data time stamps. When programs
are running in pipeline mode, measurements can be synchronized to within a
few microseconds. See
WaitDigTrig Scans
(p. 216).
3.
PakBus
(p. 87)
commands — the CR6 is a PakBus device, so it is capable of
being a node in a PakBus network. Node clocks in a PakBus network are
synchronized using the
SendGetVariable()
,
ClockReport()
, or
PakBusClock()
commands. The CR6 clock has a resolution of 1 ms , which is
the resolution used by PakBus clock-sync functions. In networks without
routers, repeaters, or retries, the communication time will cause an additional
error (typically a few 10s of milliseconds). PakBus clock commands set the
time at the end of a scan to minimize the chance of skipping a record to a data
table. This is not the same clock check process used by
LoggerNet
as it does
not use average round trip calculations to try to account for network
connection latency.
4. Radios — A PakBus enabled radio network has an advantage over Ethernet in
that
ClockReport()
can be broadcast to all dataloggers in the network
simultaneously. Each will set its clock with a single PakBus broadcast from
the master. Each datalogger in the network must be programmed with a
PakBusClock()
instruction.
Note
Use of PakBus clock functions re-synchronizes the
Scan()
instruction. Use should not exceed once per minute. CR6 clocks drift at a
slow enough rate that a
ClockReport()
once per minute should be
sufficient to keep clocks within 30 ms of each other.
With any synchronization method, care should be taken as to when and
how things are executed. Nudging the clock can cause skipped scans or
skipped records if the change is made at the wrong time or changed by
too much.
5. GPS — clocks in CR6s can be synchronized to within about 10 ms of each
other using the
GPS()
instruction. CR6s can be synchronized within a few
microseconds of each other and within ≈200 µs of UTC. While a GPS signal is
available, the CR6 essentially uses the GPS as its continuous clock source, so
the chances of jumps in system time and skipped records are minimized.
6. Ethernet — any CR6 with a network connection (internet, GPRS, private
network) can synchronize its clock relative to Coordinated Universal Time
(UTC) using the
NetworkTimeProtocol()
instruction. Precisions are usually
maintained to within 10 ms. The NTP server could be another logger or any
NTP server (such as an email server or nist.gov). Try to use a local server —
something where communication latency is low, or, at least, consistent. Also,
try not to execute the
NetworkTimeProtocol()
at the top of a scan; try to ask
for the server time between even seconds.
Summary of Contents for CR6 Series
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Page 76: ...Section 5 Overview 76 FIGURE 20 Half Bridge Wiring Example Wind Vane Potentiometer ...
Page 80: ...Section 5 Overview 80 FIGURE 23 Pulse Input Wiring Example Anemometer ...
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Page 454: ...Section 8 Operation 454 FIGURE 104 Narrow Sweep High Noise ...
Page 459: ...Section 8 Operation 459 FIGURE 106 Vibrating Wire Sensor Calibration Report ...
Page 535: ...Section 8 Operation 535 8 11 2 Data Display FIGURE 121 CR1000KD Displaying Data ...
Page 537: ...Section 8 Operation 537 FIGURE 123 CR1000KD Real Time Custom ...
Page 538: ...Section 8 Operation 538 8 11 2 3 Final Storage Data FIGURE 124 CR1000KD Final Storage Data ...
Page 539: ...Section 8 Operation 539 8 11 3 Run Stop Program FIGURE 125 CR1000KD Run Stop Program ...
Page 541: ...Section 8 Operation 541 FIGURE 127 CR1000KD File Edit ...
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Page 610: ...Section 11 Glossary 610 FIGURE 137 Relationships of Accuracy Precision and Resolution ...
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