|
LT1025 の電気的特性と機能
|
LT1025のメーカーはLinear Technologyです、この部品の機能は「Micropower Thermocouple Cold Junction Compensator」です。 |
|
|
製品の詳細 ( Datasheet PDF )
| 部品番号 LT1025 |
| 部品説明 Micropower Thermocouple Cold Junction Compensator |
| メーカ Linear Technology |
ロゴ |
このページの下部にプレビューとLT1025ダウンロード（pdfファイル）リンクがあります。 Total 12 pages |
No Preview Available ! |
LT1025
Micropower Thermocouple
Cold Junction Compensator
FEATURES
s 80µA Supply Current
s 4V to 36V Operation
s 0.5°C Initial Accuracy (A Version)
s Compatible with Standard Thermocouples
(E, J, K, R, S, T)
s Auxiliary 10mV/°C Output
s Available in 8-Lead PDIP and SO Packages
U
APPLICATIO S
s Thermocouple Cold Junction Compensator
s Centigrade Thermometer
s Temperature Compensation Network
DESCRIPTIO
The LT®1025 is a micropower thermocouple cold junction
compensator for use with type E, J, K, R, S, and T
thermocouples. It utilizes wafer level and post-package
trimming to achieve 0.5°C initial accuracy. Special curvature
correction circuitry is used to match the “bow” found in all
thermocouples so that accurate cold junction compensation
is maintained over a wider temperature range.
The LT1025 will operate with a supply voltage from 4V to 36V.
Typical supply current is 80µA, resulting in less than 0.1°C
internal temperature rise for supply voltages under 10V.
A 10mV/°C output is available at low impedance, in addition
to the direct thermocouple voltages of 60.9µV/°C (E),
51.7µV/°C (J), 40.3µV/°C (K, T) and 5.95µV/°C (R, S). All
outputs are essentially independent of power supply voltage.
A special kit is available (LTK001) which contains an LT1025
and a custom tailored thermocouple amplifier. The amplifier
and compensator are matched to allow a much tighter specifi-
cation of temperature error than would be obtained by adding
the compensator and amplifier errors on a worst-case basis.
The amplifier from this kit is available separately as LTKA0x.
The LT1025 is available in either an 8-pin PDIP or 8-pin SO
package for temperatures between 0°C and 70°C.
, LTC and LT are registered trademarks of Linear Technology Corporation.
BLOCK DIAGRA
BOW*
CORRECTION
VOLTAGE
E 60.9µV/°C
VIN
+
BUFFER
–
J 51.7µV/°C
K,T 40.6µV/°C
R, S 6µV/°C
10mV/°C
TEMPERATURE
SENSOR
R– COMMON
V0 10mV/°C
*CORRECTS FOR BOW
GND
IN COLD JUNCTION, NOT
IN PROBE (HOT JUNCTION)
LT1025 • BD01
TYPICAL APPLICATIO
Type K 10mV/°C Thermometer
R2
100Ω
FULL-SCALE TRIM
R3**
255k
1%
V+
VIN K
LT1025
GND R– VO
R1
1k
1%
–+
TYPE K
R4*
V–
V+
–
LTKA0x††
+
C2
0.1µF
VOUT
10mV/°C
V–
*R4
≤
V–
30µA
,
R4
IS
NOT
REQUIRED
C1 (OPEN) FOR LT1025 TEMPERATURES ≥ 0°C
0.1µF **SELECTED FOR 0°C TO 100°C RANGE
†† OR EQUIVALENT. SEE
“AMPLIFIER CONSIDERATIONS”
LT1025 • TA01
1025fb
1
1 Page
TYPICAL PERFOR A CE CHARACTERISTICS
10mV/°C Output Temperature
Error LT1025
10
8
6 GUARANTEED LIMITS*
LT1025
4
2
0
–2
–4
–6
–8
–10
–50 –25 0 25 50 75 100 125
JUNCTION TEMPERATURE (°C)
LT1025 • G01
*ERROR CURVE FACTORS IN THE NONLINEARITY
TERM BUILT IN TO THE LT1025. SEE THEORY OF
OPERATION IN APPLICATION GUIDE SECTION
10mV/°C Output Temperature
Error LT1025A
5
4
3 GUARANTEED LIMITS*
LT1025A
2
1
0
–1
–2
–3
–4
–5
–50 –25 0 25 50 75 100 125
JUNCTION TEMPERATURE (°C)
LT1025 • G02
*ERROR CURVE FACTORS IN THE NONLINEARITY
TERM BUILT IN TO THE LT1025. SEE THEORY OF
OPERATION IN APPLICATION GUIDE SECTION
LT1025
Supply Current
200
DOES NOT INCLUDE 30µA
180 PULL-DOWN CURRENT
160
REQUIRED FOR TEMPERATURES
BELOW 0°C
140
TJ = 125°C
120
100
80
TJ = 25°C
60
40
20 TJ = –55°C
PIN 4 TIED TO PIN 5
0
0 5 10 15 20 25 30 35 40
SUPPLY VOLTAGE (V)
LT1025 • G03
APPLICATIO S I FOR ATIO
The LT1025 was designed to be extremely easy to use, but
the following ideas and suggestions should be helpful in
obtaining the best possible performance and versatility
from this new cold junction compensator.
Theory of Operation
A thermocouple consists of two dissimilar metals joined
together. A voltage (Seebeck EMF) will be generated if the
two ends of the thermocouple are at different
temperatures. In Figure 1, iron and constantan are joined
at the temperature measuring point T1. Two additional
thermocouple junctions are formed where the iron and
constantan connect to ordinary copper wire. For the
purposes of this discussion it is assumed that these two
junctions are at the same temperature, T2. The Seebeck
voltage, VS, is the product of the Seebeck coefficient α,
and the temperature difference, T1 – T2; VS = α (T1 – T2).
The junctions at T2 are commonly called the cold junction
because a common practice is to immerse the T2 junction
in 0°C ice/water slurry to make T2 independent of room
temperature variations. Thermocouple tables are based
on a cold-junction temperature of 0°C.
To date, IC manufacturers efforts to make microminiature
thermos bottles have not been totally successful. There-
fore, an electronically simulated cold-junction is required
for most applications. The idea is basically to add a
temperature dependent voltage to VS such that the voltage
sum is the same as if the T2 junction were at a constant 0°C
instead of at room temperature. This voltage source is
called a cold junction compensator. Its output is designed
to be 0V at 0°C and have a slope equal to the Seebeck
coefficient over the expected range of T2 temperatures.
TEMPERATURE T1
TO BE MEASURED
Fe
CONSTANTAN
T2
Figure 1
Cu
}VS
Cu
LT1025 MUST BE LOCATED
NEXT TO COLD JUNCTION
FOR TEMPERATURE TRACKING
LT1025 • AG01
To operate properly, a cold junction compensator must be
at exactly the same temperature as the cold junction of the
thermocouple (T2). Therefore, it is important to locate the
LT1025 physically close to the cold junction with local
temperature gradients minimized. If this is not possible,
1025fb
3
3Pages
LT1025
APPLICATIO S I FOR ATIO
In many situations, thermocouples are used in high noise
environments, and some sort of input filter is required.
(See discussion of input filters). To reject 60Hz pick-up
with reasonable capacitor values, input resistors in the
10k-100k range are needed. Under these conditions, bias
current for the amplifier needs to be less than 1nA to avoid
offset and drift effects.
To avoid gain error, high open loop gain is necessary for
single-stage thermocouple amplifiers with 10mV/°C or higher
outputs. A type K amplifier, for instance, with 100mV/°C
output, needs a closed loop gain of ≈2,500. An ordinary op
amp with a minimum open loop of 50,000 would have an
initial gain error of (2,500)/(50,000) = 5%! Although closed
loop gain is commonly trimmed, temperature drift of open
loop gain will have a very deleterious effect on output
accuracy. Minimum suggested open loop gain for type E, J,
K, and T thermocouples is 250,000. This gain is adequate for
type R and S if output scaling is 10mV/°C or less.
Suggested Amplifier Types
THERMOCOUPLE
E, J, K, T
±15V
LTKA0x
LT1012
LT1001
SUPPLY VOLTAGE
±5V SINGLE SUPPLY
LTKA0x
LT1012
LT1001
LTC1050
LTC1052
LT1006
LTC1050
LTC1052
LT1006
R, S
LTKA0x
LTC1050
LTC1050
LT1012
LTC1052
LTC1052
LTKA0x
LT1006
Thermocouple Nonlinearities
Thermocouples are linear over relatively limited temperature
spans if accuracies of better than 2°C are needed. The graph
in Figure 4 shows thermocouple nonlinearity for the
temperature range of 0°C to 400°C. Nonlinearities can be
dealt with in hardware by using offsets, breakpoints, or power
series generators. Software solutions include look-up tables,
power series expansions, and piece-wise approximations.
For tables and power series coefficients, the reader is referred
to the ASTM Publication 470A.
Hardware correction for nonlinearity can be as simple as an
offset term. This is shown in Figure 5. The thermocouple
shown in the figure has an increasing slope (α) with
6
0 K→SCALE
2.5
5
7.5 J→SCALE
10
12.5 SCALE←E
15
17.5
20 SCALE←T
0
1
2
3
4
5
6
7
8
0 50 100 150 200 250 300 350 400
TEMPERATURE (°C)
LT1025 • G04
Figure 4. Thermocouple Nonlinearity, 0°C to 400°C
ERROR BEFORE OFFSETTING
VH
ERROR AFTER OFFSETTING
OFFSET AMPLIFIER
SIMPLE AMPLIFIER
THERMOCOUPLE
VL
0
TL T1/6 TM
T5/6 TH
TEMPERATURE (°C)
LT1025 • G05
Figure 5. Offset Curve Fitting
temperature. The temperature range of interest is between TL
and TH, with a calibration point at TM. If a simple amplifier is
used and calibrated at TM, the output will be very high at TL
and very low at TH. Adding the proper offset term and
calibrating at T1/6 or T5/6 can significantly reduce errors. The
technique is as follows:
1. Calculate amplifier gain:
G = (SF) (TH – TL)/(VH – VL)
SF = Output scale factor, e.g., 10mV/°C
VH = Thermocouple output at TH
VL = Thermocouple output at TL
2. Use precision resistors to set gain or calibrate gain by
introducing a precision “delta” input voltage and trimming
for proper “delta” output.
1025fb
6 Page
合計 : 12 ページ |
| PDF ダウンロード [ LT1025 データシート.PDF ] |
|
データシートを活用すると、その部品の主な機能と仕様を詳しく理解できます。 ピン構成、電気的特性、動作パラメータ、性能を確認してください。 |
|
|
| 部品番号 | 部品説明 | メーカ |
| LT102 | LT Series: 25/30 WATT Wide Input Range |  ETC |
| LT1020 | Micropower Regulator and Comparator | Linear Technology |
| LT1021 | Precision Reference | Linear Technology |
| LT1022 | High Speed / Precision JFET Input Operational Amplifier | Linear Technology |