Campbell Scientific CR1000KD CR1000 Measurement and Control System - Page 254

PRTCalc, Table 45., PRTCalc Type-Code-1 Sensor

Page 254 highlights

Section 7. Installation 254 non-standard types. Measured temperatures are compared against the ITS-90 scale, a temperature instrumentation-calibration standard. PRTCalc() follows the principles and equations given in the US ASTM E1137-04 standard for conversion of resistance to temperature. For temperature range 0 to 650 °C, a direct solution to the CVD equation results in errors < ±0.0005°C (caused by rounding errors in CR1000 math). For the range of -200 to 0°C, a fourth-order polynomial is used to convert resistance to temperature resulting in errors of < ±0.003°C. These errors are only the errors in approximating the relationships between temperature and resistance given in the relevant standards. The CVD equations and the tables published from them are only an approximation to the true linearity of an RTD, but are deemed adequate for industrial use. Errors in that approximation can be several hundredths of a degree Celsius at different points in the temperature range and vary from sensor to sensor. In addition, individual sensors have errors relative to the standard, which can be up to ±0.3°C at 0°C with increasing errors away from 0°C, depending on the grade of sensor. Highest accuracy is usually achieved by calibrating individual sensors over the range of use and applying corrections to the RS/RO value input to the PRTCalc() instruction (by using the calibrated value of RO) and the multiplier and offset parameters. Refer to CRBasic Editor Help for specific PRTCalc() parameter entries. The following information is presented as detail beyond what is available in CRBasic Editor Help. The general form of the Callendar-Van Dusen (CVD) equation is: R/R =1: T = (SQRT(d * (R/R ) + e) -a) / f 0 0 Depending on the code entered for parameter Type, which specifies the platinum- resistance sensor type, coefficients are assigned values according to the following tables. Note Coefficients are rounded to the seventh significant digit to match the CR1000 math resolution. Note Alpha is defined as (R100/R0-1)/100, where R100 and R0 are the resistances of the PRT at 100°C and 0°C, respectively. Table 45. PRTCalc() Type-Code-1 Sensor IEC 60751:2008 (IEC 751), alpha = 0.00385. Now internationally adopted and written into standards ASTM E1137-04, JIS 1604:1997, EN 60751 and others. This type code is also used with probes compliant with older standards DIN43760, BS1904, and others. (Reference: IEC 60751. ASTM E1137) Constant Coefficient a 3.9083000E-03 d -2.3100000E-06

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Section 7.
Installation
254
non-standard types. Measured temperatures are compared against the ITS-90
scale, a temperature instrumentation-calibration standard.
PRTCalc()
follows the principles and equations given in the US ASTM E1137-04
standard for conversion of resistance to temperature.
For temperature range 0 to
650 °C, a direct solution to the CVD equation results in errors < ±0.0005°C
(caused by rounding errors in CR1000 math).
For the range of -200 to 0°C, a
fourth-order polynomial is used to convert resistance to temperature resulting in
errors of < ±0.003°C.
These errors are only the errors in approximating the relationships between
temperature and resistance given in the relevant standards. The CVD equations
and the tables published from them are only an approximation to the true linearity
of an RTD, but are deemed adequate for industrial use. Errors in that
approximation can be several hundredths of a degree Celsius at different points in
the temperature range and vary from sensor to sensor. In addition, individual
sensors have errors relative to the standard, which can be up to ±0.3°C at 0°C with
increasing errors away from 0°C, depending on the grade of sensor. Highest
accuracy is usually achieved by calibrating individual sensors over the range of
use and applying corrections to the R
S
/R
O
value input to the
PRTCalc()
instruction (by using the calibrated value of R
O
) and the multiplier and offset
parameters.
Refer to
CRBasic Editor Help
for specific
PRTCalc()
parameter entries.
The
following information is presented as detail beyond what is available in
CRBasic
Editor Help
.
The general form of the Callendar-Van Dusen (CVD) equation is:
R/R
0
<1: T = g * K^4 + h * K^3 + I * K^2 + j * K, where K =
R/R
0
– 1
R/R
0
>=1: T = (SQRT(d * (R/R
0
) + e) -a) / f
Depending on the code entered for parameter
Type
, which specifies the platinum-
resistance sensor type, coefficients are assigned values according to the following
tables.
Note
Coefficients are rounded to the seventh significant digit to match the
CR1000 math resolution.
Note
Alpha is defined as (R
100
/R
0
-1)/100, where R
100
and R
0
are the resistances of
the PRT at 100°C and 0°C, respectively.
Table 45.
PRTCalc() Type-Code-1 Sensor
IEC 60751:2008 (IEC 751), alpha = 0.00385.
Now internationally
adopted and written into standards ASTM E1137-04, JIS 1604:1997,
EN 60751 and others.
This type code is also used with probes
compliant with older standards DIN43760, BS1904, and others.
(Reference: IEC 60751. ASTM E1137)
Constant
Coefficient
a
3.9083000E-03
d
-2.3100000E-06