Campbell Scientific CR3000 CR3000 Micrologger - Page 292
Minimizing Settling Errors
View all Campbell Scientific CR3000 manuals
Add to My Manuals
Save this manual to your list of manuals |
Page 292 highlights
Section 8. Operation The CR3000 delays after switching to a channel to allow the input to settle before initiating the measurement. The SettlingTime parameter of the associated measurement instruction is provided to allow the user to tailor measurement instruction settling times with 100 µs resolution up to 35000 µs. Default settling times are listed in table CRBasic Measurement Settling Times (p. 292), and are meant to provide sufficient signal settling in most cases. Additional settling time may be required when measuring high-resistance (high-impedance) sensors and / or sensors connected to the datalogger by long leads. Measurement time of a given instruction increases with increasing settling time. For example, a 1 ms increase in settling time for a bridge instruction with input reversal and excitation reversal results in a 4 ms increase in time for the CR3000 to perform the instruction. Table 59. CRBasic Measurement Settling Times Settling Time Entry Input Voltage Range Integration Code Settling Time1 0 All 250 200 µs (default) 0 All _50Hz 3 ms (default) 0 All >100 All _60Hz X2 3 ms (default) μs entered 1Minimum settling time required to allow the input to settle to CR3000 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 CR3000 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 CR3000. 292