Campbell CR800 Series, Руководство оператора

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Section 7. Installation
275
Rs/R0, K, and temperature
Rs/R0 = –(R4/((R4*X3
CAL
)/(1–X3
CAL
)))*(Xp/(Xp – 1))
K = (Rs/R0) –1
T = (SQRT(d * (R/R0) + e) – a) / f (see PRT Calculation Standards for
coefficients)
or
T = g * K^4 + h * K^3 + I * K^2 + j * K (see PRT Calculation Standards for
coefficients)
Resistance of the PRT (R3) :
R3 = (R 4 • X3)/(1 – X3)
X3 = (X / 1000) + (R2/(R1 + R2))
Measurement resolution:
There is a change of approximately 2 mV from the output at 40 °C to the
output at 51 °C, or 200 µV / °C. With a resolution of 0.33 µV on the ±25
mV range, this means that the temperature resolution is 0.0009 °C.
7.7.16.6 PRT Callendar-Van Dusen Coefficients
As shown in the preceding PRT measurement examples, use the PRTCalc()
instruction in the CRBasic program to process PRT resistance measurements.
NOTE PRT() (not PRTCalc() ) is obsolete.
PRTCalc() uses the following inverse Callendar-Van Dusen equations to
calculate temperature from resistance.
For temperatures <0 °C:
T = g • K • j + K
2
• i + K
3
• h + K
4
, wher e K = R
S
/R
0
– 1 (Eq. 1)
For temperatures ≥0 °C:
T = (sqrt(d • R
S
/R
0
+ e) – a) / f (Eq. 2)
Eq.1 conforms to US ASTM E1137-04 standard for conversion of resistance to
temperature. For temperatures 0 to 650 °C, it introduces <±0.0005 °C error to
the measurement. The source of the error is rounding errors in CR800 math.
Eq. 2 is derived from US ASTM E1137-04 and conforms to other industry
standards. For temperatures –200 to 0 °C, it introduces < ±0.003 °C error to the
measurement.