Campbell Scientific CR1000KD CR800 and CR850 Measurement and Control Systems - Page 283
Minimizing Settling Errors, 1.2.8.2 Measuring the Necessary Settling Time
View all Campbell Scientific CR1000KD manuals
Add to My Manuals
Save this manual to your list of manuals |
Page 283 highlights
Section 8. Operation Table 57. CRBasic Measurement Settling Times Settling Time Entry Input Voltage Range Integration Code Settling Time1 0 All 250 450 µs (default) 0 All _50Hz 3 ms (default) 0 All _60Hz 3 ms (default) >100 All X2 μs entered 1Minimum settling time required to allow the input to settle to CR800 resolution specifications. 2X is an integer >100. A settling time is required for voltage measurements to minimize the effects of the following sources of error: • A small switching transient occurs when the CR800 switches to the singleended or differential channel to be measured. • A relatively large transient may be induced on the signal conductor via capacitive coupling during a bridge measurement from an adjacent excitation conductor. • 50-Hz or 60-Hz integrations require a relatively long reset time of the internal integration capacitor before the next measurement due to dielectric absorption. 8.1.2.8.1 Minimizing Settling Errors When long lead lengths are required the following general practices can be used to minimize or measure settling errors: • Do not use wire with PVC-insulated conductors. PVC has a high dielectric, which extends input settling time. • Where possible, run excitation leads and signal leads in separate shields to minimize transients. • When measurement speed is not a prime consideration, additional time can be used to ensure ample settling time. The settling time required can be measured with the CR800. • 8.1.2.8.2 Measuring the Necessary Settling Time Settling time for a particular sensor and cable can be measured with the CR800. Programming a series of measurements with increasing settling times will yield data that indicate at what settling time a further increase results in negligible change in the measured voltage. The programmed settling time at this point indicates the true settling time for the sensor and cable combination. CRBasic example Measuring Settling Time (p. 284) presents CRBasic code to help determine settling time for a pressure transducer utilizing a high-capacitance semi-conductor. The code consists of a series of full-bridge measurements (BrFull()) with increasing settling times. The pressure transducer is placed in 283