Calibration check 7828 Density Transmitter Technical Manual
5-2 78285000_AA
c. Temperature coefficient data; this defines the correction which should be applied to
achieve the best accuracy if the instrument is operating at product temperatures other
than 20°C.
d. One instrument air data point for check calibration purposes.
5.1.4 GENERAL DENSITY EQUATION
The General Density Equation, used to calibrate the 7828 and shown in the Calibration
certificate is:
ρ = K0 + K1τ + K2τ
2
where ρ is the calculated density, τ is the time period (in µs) of the tuning fork, and K0, K1
and K2 are density coefficients.
When the 7828 is calibrated in a known environment, K0, K1 and K2 are selected to
optimise the density measurement across the calibrated density range.
As you can also see in the sample calibration certificate, temperature effects are also
compensated for using a second equation:
ρ’ = ρ( 1 + K18(t - 20)) + K19(t - 20)
where
ρ’ is the new (temperature compensated) density value, t is the measurement
temperature, and K18 and K19 are temperature correction coefficients.
The values for all the K coefficients - shown on the calibration certificate - are
programmed into the 7828’s registers, and should not be altered.
If the 7828 is used in an application dissimilar to the one for which it was originally
calibrated, it may be necessary to re-calculate the K coefficients. Contact Solartron for
further details.
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