Yokogawa Wireless Temperature Transmitter YTA510 - Manual (Page 36)

IM 01C50T03-01E B-1
APPENDIX B. THE SENSOR MATCHING FUNCTION
APPENDIX B. THE SENSOR MATCHING
FUNCTION
B.1 Specifications
Function: The sensor-specific constants can be pro-
grammed into the transmitter.
Applicable model: YTA310 /CM1, YTA320 /CM1
RTD sensor: Pt100, Pt200, Pt500
Significant temperature measurement accuracy im-
provement can be attained using a temperature sensor
that is matched to a temperature transmitter. This
matching process entails teaching the temperature
transmitter the relationship between resistance and
temperature for a specific RTD sensor. This relation-
ship, approximated by the Callendar-Van Dusen
equation, is described as:
Rt = R0 {1 +
␣ ( 1 + 0.01␦ ) t - ␣␦ / 10
4 t 2 -
␣␤ / 10
8
( t - 100 ) t 3 }
where: Rt = Resistance (ohms) at Temperature t (
ЊC)
R0 = Sensor - Specific Constant
(Resistance at t = 0
ЊC)
␣ = Sensor - Specific Constant
␦ = Sensor - Specific Constant
␤ = Sensor - Specific Constant (0 at t > 0 ЊC)
The exact values for R0 ,
␣, ␦, and ␤ are specific to
each RTD sensor, and are obtained by testing each
individual sensor at various temperatures. These
constants are known as Callendar-Van Dusen con-
stants.
Generally the constants R0, A, B, and C are also being
used as the characteristic coefficients of the sensor
instead of R0,
␣, ␦, and ␤. These are derived from the
IEC Standard Curve and the relationship is described
as:
Rt = R0 [ 1 + At + Bt 2 + C ( t - 100 ) t 3 ]
where: Rt = Resistance (ohms) at Temperature t (
ЊC)
R0 = Sensor - Specific Constant
(Resistance at t = 0
ЊC)
A = Sensor - Specific Constant
B = Sensor - Specific Constant
C = Sensor - Specific Constant (0 at t > 0
ЊC)
These two equations are equivalent. A model YTA can
cope with either case above-mentioned.
IMPORTANT
There is the following limitations for R0,
␣
,
␦
,
␤
,
A, B, and C with the YTA.
•
IT is necessary to enter the value, which is
normalized by the exponential part specified
for each parameter. See Table B.1.
• It is necessary to enter the value, which is
rounded off to three or two decimal places
specified for each parameter. See Table B.1.
• When a three decimal place data is entered,
it may be automatically changed to the four
decimal place data that is equivalent to the
input data.
Example: +3.809 E-3
→
+3.8089 E-3
Table B.1
T0B01.EPS
Item
Number of
decimal
places
exponential
part
Input
Example
Factory
Initial
R0
A
B
C
␣
␦
␤
2
3
3
3
3
3
3
non
E-3 (10 -3 )
E-7 (10 -7 )
E-12 (10 -12 )
E-3 (10 -3 )
E0 (10 0 )
E-1 (10 -1 )
+ 100.05
+ 3.908 E-3
- 5.802 E-7
- 0 E-12
+ 3.850 E-3
+ 1.507 E0
+ 0 E-1
+100
+3.9083 E-3
-5.7749 E-7
-4.183 E-12
+3.8505 E-3
+1.4998 E0
+1.0862 E-1