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Temperature Sensor_Thermocouples Selection guide
Temperature Sensor_Thermocouples Selection guide
1. Complete Assebly / Element Only / Well Only
A. Display the parts that the vendor needs to supply
i. Complete Assembly: Thermocouple (hereinafter referred to as T/C), Themowell (hereinafter referred to as T/W) and other ancillary devices are consistently included
ii. Element Only: When purchasing T/C only
2. Element Type
A. T/C is standardized according to the temperature range, and T/C is selected and used according to the desired temperature range.
In general, “K” Type is used a lot.
i. T/C Type Classification
Type E
Temperature Range: -200 to 900 deg.C
Meaterial: Chromel / Constantan
Feature: Used at medium temperature, less accurate than K
J
Temperature Range:0 to 750 deg.C
Meaterial:Iron / Constantan
Feature: It is easy to oxidize above 500 degrees, and the compensating wire is cheap.
K
Temperature Range:-200 to 1250 deg.C
Meaterial: Chromel / Alumel
Feature: Widely used, but weak to reducing atmosphere and sulfurous gas
R
Temperature Range:0 to 1650 deg.C
Meaterial: Pt-13% Rhodium / Pt
Feature: High temperature measurement and good precision, but expensive and weak
S
Temperature Range:0 to 1650 deg.C
Meaterial: Pt-10% Rhodium / Pt
Feature: High temperature measurement and good precision, but expensive and weak
T
Temperature Range: -200 to 350 deg.C
Meaterial: Copper / Constantan
Feature: Use at low temperatures as stability is maintained at low temperatures
★ After selecting the T/C, the compensating wire must be selected and connected with the same material as the T/C so that there is no error in the measured temperature value. For example, if K Type T/C is selected and a general signal cable or a different type of compensation wire is used instead of the compensation wire, the temperature value checked in the system is displayed differently.
3. Sheath
A. The part that is wrapped to protect the element
i. O.D (Out diameter): It refers to the outer diameter of the sheath, and 6.4mm is usually used.
ii. Material: Generally, 304SS and 316SS are used, and the material varies depending on the fluid used.
iii. Grounding Type
- Type of Measuring Junction (Grounding between Wire and Sheath)
Ungrounded Tpye is mainly used, and there are three types: Exposed, Grounded, and Un-grounded.
: Response speed: Exposed < Un-grounded < Grounded
: Induced disturbance effect: Exposed > Un-grounded > Grounded
: Chemical stability: Exposed < Un-grounded < Grounded
: Mechanical strength: Exposed < Un-grounded < Grounded
iv. Spring Loaded: The function of attaching the sheath close to the bottom of the well with spring force to maximize heat transfer between the sheath junction and the well.
Considering the above considerations, T/C can be selected according to the intended use. In particular, it is necessary to select the appropriate T/C in consideration of the temperature range and the material of the fluid.
1. Complete Assebly / Element Only / Well Only
A. Vendor가 공급해야할 부분을 구분하여 표시
i. Complete Assembly: Thermocouple(이하 T/C), Themowell(이하 T/W) 및 기타 부수적 장치가 일관 포함
ii. Element Only: T/C만 구매할 경우
2. Element Type
A. 온도 범위에 따라 T/C를 규격화 한 것으로, 사용하고자 하는 온도범위에 맞게 T/C를 선정하여 사용한다.
일반적으로 “K” Type이 많이 사용된다.
i. T/C Type 분류
Type 온도범위 재질 특징 E -200 to 900 deg.C Chromel / Constantan 중간온도에서 사용 , K 보다 정확도 떨어짐 J 0 to 750 deg.C Iron / Constantan 500 도 이상에서 산화되기 쉬움 , 보상도선 값이 저렴함 K -200 to 1250 deg.C Chromel / Alumel 광범위하게 사용되나 환원분위기 , 아황상 가스등에 약함 R 0 to 1650 deg.C Pt-13% Rhodium / Pt 높은 온도측정 및 정도가 좋으나 값이 비싸고 약함 S 0 to 1650 deg.C Pt-10% Rhodium / Pt 높은 온도측정 및 정도가 좋으나 값이 비싸고 약함 T -200 to 350 deg.C Copper / Constantan 저온에서 안정성이 유지되므로 저온에서 사용
★ T/C 선정 후 반드시 보상도선도 동일한 T/C와 동일한 재질로 선정해서 연결해야 측정된 온도 값에 오류가 없다. 예를 들어 K Type T/C를 선정하고 보상도선이 아닌 일반 신호케이블 또는 다른 Type의 보상도선을 사용하게 된다면 시스템에서 확인되는 온도값이 다르게 나타단다.
3. Sheath
A. Element를 보호하기 위해 감싸고 있는 부분
i. O.D(Out diameter): Sheath의 외경을 말하며 보통 6.4mm를 많이 사용한다.
ii. Material: 일반적으로 304SS, 316SS를 사용하며 사용되는 유체에 따라 Material이 달라진다.
iii. Grounding Type
- Measuring Junction의 형태(Wire 와 Sheath간의 접지형태)
Ungrounded Tpye이 주로 쓰이며, Exposed, Grounded, Un-grounded 세가지 Type이 있다.
: 응답속도: Exposed < Un-grounded < Grounded
: 유도장해 영향: Exposed > Un-grounded > Grounded
: 화학적 안정성: Exposed < Un-grounded < Grounded
: 기계적 강도: Exposed < Un-grounded < Grounded
iv. Spring Loaded: Sheath Junction과 Well과의 열전달을 극대화 하기위해 Sheath를 Spring 힘으로 Well 바닥에 가까이 밀착 시키는 기능.
상기 고려사항을 고려하여 T/C를 사용 용도에 맞게 선정 할 수 있다. 특히 온도범위, 유체 재질을 꼭 고려하여 알맞은 T/C를 선택해야 한다.
from http://freedomrj.tistory.com/10 by ccl(A) rewrite - 2021-12-19 08:28:23