Wavelength Electronics LFI-3751, Руководство пользователя, Страница: 36 / 132

Ω
P ACT T
LIM I
AUX T
TE V
SET T
TE I
B
C
I
A
D
°
C
k
decrease
increase
P ACT T
LIM I
AUX T
TE V
SET T
TE I
B
C
I
A
D
Adjust A
Enter T
1
[A1]
Enter R
1
[A2]
4. Entering Data Pair - A
•
Rotate the Display Select Switch to A ( Shift Button ON ).
The fi rst two data pairs alternate on the display. One is
temperature (
°C LED lit), the other is the corresponding
thermistor resistance ( k
Ω
LED lit).
•
Rotate the Digi-Pot Adjust Knob to change the value
displayed. Default from the factory sets up for a 10 k
Ω
thermistor (Wavelength part number TCS-610).
•
To display thermistor resistance rather than temperature,
enter (0.000, 0.000) for the A terms. [ B & C are ignored
for resistance display.]
•
A, B, and C cannot be adjusted while the output is on.
•
Data pairs A , B , and C are saved in non-volatile memory.
•
RS-232 Command: [A1] = T
1
, [A2] = R
1
Chapter 2 - Front Panel Operation
Controlling Temperature with Thermistors
36
3. Thermistor Temperature vs. Resistance
Temperature can be determined by the Steinhart-Hart equation
given the thermistor resistance and the equation coeffi cients
χ
1
,
χ
2
, and
χ
3
.
To calculate the Steinhart-Hart coeffi cients, the LFI-3751 needs
three (Temperature, Resistance) data pairs. Enter
A : ( T
1
, R
1
),
B : ( T
2
, R
2
), and C : ( T
3
, R
3
) through the front panel or [A1], [A2],
[B1], [B2], [C1], and [C2] via the RS-232 interface. Using the
thermistor resistance vs. temperature chart provided with your
thermistor, select three temperatures. These temperatures
can be far apart if you’re working with a wide temperature
range, or close together to optimize the curve fi t around one
temperature.
1
T
=
χ
1
+
χ
2
ln(R) +
χ
3
(ln(R)) 3
Steinhart-Hart Equation
Typical Thermistor
R vs. T response
T = Temperature (Kelvin)
R = Resistance (Ohms)
Display Resolution:
Temperature
Resistance
-199.9
-19.99
-1.999
10.00
100.0
0
10.00
100.0
to
to
to
to
to
to
to
to -20.0°C
-2.00°C
9.999°C
99.99°C
199.9°C
9.999 k
Ω
99.99 k
Ω
499.9 k
Ω
0
5
10
15
20
25
30
35
0 10 20 30 40 50
Temperature ° C
T1, R1
T2, R2
T3, R3
Resistance k Ω