Campbell Scientific CR3000 Micrologger - Manual (Page 332)

Section 8. Operation
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With any synching 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 CR3000s can be synchronized to within about 10 ms of each
other using the GPS() instruction. CR3000s built since October of 2008
(serial numbers ≥ 3168) can be synchronized within a few microseconds of
each other and within ≈200 µs of UTC. While a GPS signal is available, the
CR3000 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 CR3000 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.
8.2 Measurement and Control Peripherals
Peripheral devices expand the CR3000 input / output capacity. Classes of
peripherals are discussed below according to use. Some peripherals are designed
as SDM (synchronous devices for measurement) devices. SDM devices are
intelligent peripherals that receive instruction from and send data to the CR3000
over a proprietary, three-wire serial communications link utilizing channels SDM-
C1, SDM-C2 and SDM-C3.
Read More! For complete information on available measurement and control
peripherals, go to the appendix Sensors and Peripherals
,
www.campbellsci.com, or
contact a Campbell Scientific applications engineer.
8.2.1 Analog-Input Expansion Modules
Mechanical relay and solid-state relay multiplexers are available to expand the
number of analog sensor inputs. Multiplexers are designed for single-ended,
differential, bridge-resistance, or thermocouple inputs.
8.2.2 Pulse-Input Expansion Modules
Pulse-input expansion modules are available for switch-closure, state, pulse-count
and frequency measurements, and interval timing.
8.2.3 Serial-Input Expansion Modules
Capturing input from intelligent serial-output devices can be challenging. Several
Campbell Scientific serial I/O modules are designed to facilitate reading and
parsing serial data. Campbell Scientific recommends consulting with an
applications engineer when deciding which serial-input module is suited to a
particular application.