Campbell Scientific CR6 CR6 Measurement and Control System - Page 369
Measurement and Control Peripherals - Details, Analog-Input Modules
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Section 8. Operation 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. 8.2 Measurement and Control Peripherals - Details Reading List: • Measurement and Control Peripherals - Overview (p. 81) • Measurement and Control Peripherals - Details (p. 369) • Measurement and Control Peripherals - Lists (p. 595) Peripheral devices expand the CR6 input and output capacities. Some peripherals are designed as SDM (synchronous devices for measurement) or CDM (CPI devices for measurement). SDM and CDM devices are intelligent peripherals that receive instruction from, and send data to, the CR6 using proprietary communication protocols through SDM terminals and CPI ports. The following sections discuss peripherals according to measurement types. 8.2.1 Analog-Input Modules Read More For more information see appendix Analog-Input Modules List (p. 596). Mechanical and solid-state multiplexers are available to expand the number of analog sensor inputs. Multiplexers are designed for single-ended, differential, bridge-resistance, or thermocouple inputs. 369
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