Specifications

Section 3. CR3000 Measurement Details
A differential measurement has the option of reversing the inputs to cancel
offsets as described above.
Sustained voltages in excess of ±16 V will damage the CR3000
circuitry.
NOTE
3.3 Signal Settling Time
Whenever an analog input is switched into the CR3000 measurement circuitry
prior to making a measurement, a finite amount of time is required for the
signal to stabilize at it's correct value. The rate at which the signal settles is
determined by the input settling time constant which is a function of both the
source resistance and input capacitance.
The CR3000 delays after switching to a channel to allow the input to settle
before initiating the measurement. The default delays used by the CR3000
depend on the integration used and the voltage range. The default delay is 450
µs for 250 µs integrations and 3 ms for 50 Hz or 60 Hz rejection integrations.
This settling time is the minimum required to allow the input to settle to the
resolution specification.
Additional wire capacitance associated with long sensor leads can increase the
settling time constant to the point that measurement errors may occur. There
are three potential sources of error which must settle before the measurement is
made:
1. The signal must rise to its correct value.
2. A small transient caused by switching the analog input into the
measurement circuitry must settle.
3. When a resistive bridge measurement is made using a switched excitation
channel, a larger transient caused when the excitation is switched must
settle.
3.3.1 Minimizing Settling Errors
When long lead lengths are mandatory, the following general practices can be
used to minimize or measure settling errors:
1. DO NOT USE WIRE WITH PVC INSULATED CONDUCTORS. PVC
has a high dielectric which extends input settling time.
2. Where possible run excitation leads and signal leads in separate shields to
minimize transients.
3. 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.
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