<3. Parameter Setting >
3-22
IM 01C50T01-02EN
The following relation exists between the resistance
(Rt) of a RTD sensor and the temperature (t) at that
time.
Rt=R0{1+α(1+0.01δ)t - αδ/10
4
t
2
- αβ/10
8
(t -100)t
3
}
where: Rt=Resistance (ohms) at Temperature t (°C)
R0=Sensor -specific constant (Resistance at t=0°C)
α (alpha)=Sensor-specific constant
δ (delta)=Sensor-specific constant
β (beta)=Sensor-specific constant
(0 at t>0°C)
Although the sensor curve is standardized, the
exact values for R0, α, δ and β are specific to each
RTD sensor and are obtained by testing each
individual sensor at various temperatures. These
constants are known as Callender-van Dusen
constants. Generally, the constants R0, A, B, and
C are also used as the characteristic coefficients
of the RTD instead of R0, α, δ and β. These
are derived from IEC Standard Curve and the
relationship is described as followings;
R
t
= R
0
{1 + At - Bt
2
+ C (t -100) t
3
}
where: Rt=Resistance (ohms) at Temperature t (°C)
R
0
= Sensor-specific constant
(Resistance at t=0°C)
A = Sensor-specific constant
B = Sensor-specific constant
C =Sensor-specific constant
(0 at t > 0°C)
These two equations are equivalent. A model YTA
can cope with either case as above-mentioned.
IMPORTANT
Note the following restrictions when inputting
values for the R0, α, δ, β, A, B, and C constants
in the YTA.
• Values must be normalized ones with an
exponential part determined for respective
constants (see the table below).
• Values must be rounded off so that they have
the digits after the decimal point determined
for respective constants (see the table
below).
• Values with three digits after the decimal
point may be changed to values with
four digits after the decimal point, which
are equivalent to the original value when
rounded off.
Example: +3.809 E-3 → +3.8089 E-3
Item
Decimal
point
Exponent
Example
Initial setting
R0
2
non
+100.05
+100
A
3
E-3 (10
-3
)
+3.908 E-3 +3.9083 E-3
B
3
E-7 (10
-7
)
-5.802 E-7 -5.7749 E-7
C
3
E-12 (10
-12
)
-0 E-12
-4.183 E-12
α
3
E-3 (10
-3
)
+3.850 E-3 +3.8505 E-3
δ
3
E0 (10
0
)
+1.507 E0 +1.4998 E0
β
3
E-1 (10
-1
)
+0 E-1
+1.0862 E-1
IMPORTANT
• This function is effective only in four kinds of
sensors; Pt100, Pt200, Pt500 and Pt1000.
• Input relations between the sensor type and
the value of R0 properly. When Pt100 is
specified as an input type, the value close
to 100 must be set to R0. When Pt500 is
specified as an input type, the value close to
500 must be set to R0.
• When the sensor type is changed, the
sensor matching function must be set up
again.
a) Setting the Sensor Matching Function
1) Device setup → Basic Setup → Sensor Basic
Setup → Sensor1 Basic Setup → set Sns1
Probe(M)
Set the sensor type to “calibrated RTD” and the
number of wires.
2) Procedure to call up the display.
Device setup → Basic setup → Sensor Basic
Setup → Sensor1 Basic Setup → Sensor1
Probe Setup → set Sns1 Matching
Set the Sns1 Matching and set the co-efficient
according to the message.
b) For Setting up two sensors
If using the sensor2, repeat the procedures for
the Sensor1.
• Procedures to call up the display
Device setup → Basic setup → Sensor Basic
Setup → Sensor2 Basic Setup → Sensor2
Probe Setup → set Sns2 Matching
NOTE
When the co-efficient of sensor matching is set
incorrectly, inverse caluculation alarm may be
generated.
