Section 5. System Overview
operating temperatures and aging. With auto-calibration disabled, measurement
accuracy over the operational temperature range is specified as less accurate by a
factor of 10. That is, over the extended temperature range of –40 °C to 85 °C, the
accuracy specification of ±0.12% of reading can degrade to ±1% of reading with
auto-calibration disabled. If the temperature of the CR1000 remains the same,
there is little calibration drift if auto-calibration is disabled. Auto-calibration can
become disabled when the scan rate is too small. It can be disabled by the
CRBasic program when using the Calibrate() instruction.
Note The CR1000 is equipped with an internal voltage reference used for
calibration. The voltage reference should be periodically checked and re-
calibrated by Campbell Scientific for applications with critical analog voltage
measurement requirements. A minimum two-year recalibration cycle is
recommended.
Unless a Calibrate() instruction is present, the CR1000 automatically auto-
calibrates during spare time in the background as an automatic slow sequence
(p.
157)
with a segment of the calibration occurring every four seconds. If there is
insufficient time to do the background calibration because of a scan-consuming
user program, the CR1000 will display the following warning at compile time:
Warning: Background calibration is disabled.
5.3.12 Maintenance — Overview
Related Topics:
• Maintenance — Overview (p. 93)
• Maintenance — Details
(p. 473)
With reasonable care, the CR1000 should give many years of reliable service.
5.3.12.1 Protection from Moisture — Overview
Protection from Moisture — Overview (p. 93)
Protection from Moisture — Details (p. 99)
Protection from Moisture — Products (p. 660)
The CR1000 and most of its peripherals must be protected from moisture.
Moisture in the electronics will seriously damage, and probably render un-
repairable, the CR1000. Water can come from flooding or sprinkler irrigation, but
most often comes as condensation. In most cases, protection from water is easily
accomplished by placing the CR1000 in a weather-tight enclosure with desiccant
and elevating the enclosure above the ground. The CR1000 is shipped with
internal desiccant packs to reduce humidity. Desiccant in enclosures should be
changed periodically.
Note Do not completely seal the enclosure if lead-acid batteries are present;
hydrogen gas generated by the batteries may build up to an explosive
concentration.
Refer to Enclosures List (p. 659) for information on available weather-tight
enclosures.
93
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