Wavelength Electronics LFI-3751, Руководство пользователя, Страница: 40 / 132

Chapter 2 - Front Panel Operation
Controlling Temperature with RTDs
40
3. RTD Temperature vs. Resistance
The LFI-3751 uses three data pairs to confi gure an RTD- A , B , and C . To
indicate you’re using an RTD, the fi rst data pair A must be (1.000, 1.000).
Enter A : (1.000, 1.000), B : ( T
1
, R
1
), and C : ( T
2
, R
2
) through the front panel
or [A1], [A2], [B1], [B2], [C1], and [C2] via the RS-232 interface. RTD
resistance changes almost linearly with temperature. Depending on your need
for accuracy, the LFI-3751 offers two methods for modeling RTDs:
Linear or
Callendar - Van Dusen Curve fi t .
Linear RTD Confi guration
The fi rst method assumes the RTD temperature response to be linear. Enter
two (Temperature, Resistance) data pairs
B : ( T
1
, R
1
) and C : ( T
2
, R
2
). R
0
(resistance at 0°C) and alpha are calculated to derive temperature from
the measured RTD resistance, R
RTD.
All resistances are in ohms and T is
in °C. Note that R
0
is typically the resistance the RTD is known by: i.e. a
“100
Ω
RTD” is usually 100
Ω
at 0°C.
R
0
= R
2
- * T
2
(R
2
- R
1
)
(T
2
- T
1
)
alpha = a =
(R
2
- R
1
)
R
0
*(T
2
- T
1
)
Linear Confi guration Constants
Linear Temperature Calculation
T
RTD
=
(R
RTD
- R
0
)
R
0
* alpha
R
0
= RTD Resistance at 0°C
(T
1
, R
1
) & (T
2
, R
2
) = B & C entries
alpha = Normalized
∆
R vs.
Temperature
R
0
= RTD Resistance at 0°C
R
RTD
= Resistance of RTD
T
RTD
= Temperature of RTD
alpha = Normalized
∆
R vs.
Temperature
Typical RTD
R vs. T response
Temperature (°C)
Resistance (
Ω
)
80
90
100
110
120
130
140
150
T1, R1
T2, R2
0
100