PT100 和 PT1000 金屬熱敏電阻感測器探頭的電阻器和電路

A temperature acquisition circuit for a PT100 or PT1000 sensor probe typically consists of a stable current source to excite the sensor, a high-precision resistance measurement circuit to detect the change in resistance with temperature, and an analog-to-digital converter (類比數位轉換器) to convert the measured voltage into a digital signal that can be processed by a microcontroller or data acquisition system; the key difference between a PT100 and PT1000 circuit is the scale of resistance values due to the Pt100 having a nominal resistance of 100 ohms at 0°C while a Pt1000 has 1000 0°C 時的歐姆, often requiring adjustments in the measurement circuit depending on the desired accuracy and application.

The article introduces the resistance change of PT100 and PT1000 metal thermal resistor sensor probes at different temperatures, as well as a variety of temperature acquisition circuit solutions. Including resistance voltage division, bridge measurement, constant current source and AD623, AD620 acquisition circuit. In order to resist interference, especially electromagnetic interference in the aerospace field, an airborne PT1000 temperature sensor acquisition circuit design is proposed, including a T-type filter for filtering and improving measurement accuracy.
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PT100 Temperature cable sensor for Precise temperature measurement in containers, tanks and pipes

溫度感測器探頭T100高溫-50～260電纜

PT100 platinum resistance temperature sensor for transmitter surface temperature

PT100/PT1000溫度擷取電路方案
1. Temperature resistance change table of PT100 and PT1000 sensors
鎳等金屬熱電阻, copper and platinum resistors have a positive correlation with the change of temperature. 鉑具有最穩定的物理和化學性質，用途最廣泛. 常用鉑電阻Pt100感知器探頭的測溫範圍為-200～850℃, Pt500的溫度測量範圍, Pt1000 感測器探頭, ETC. 都在陸續減少. 鉑1000, 溫度測量範圍-200～420℃. 依據IEC751國際標準, 鉑電阻Pt1000的溫度特性符合以下要求:

PT1000溫度特徵曲線

根據PT1000溫度特徵曲線, the slope of the resistance characteristic curve changes slightly within the normal operating temperature range (如圖 1). The approximate relationship between resistance and temperature can be obtained through linear fitting:

PT100耐溫變化表 1

2. 常用的採集電路解決方案

2. 1 Resistor voltage divider output 0~3.3V/3V analog voltage single chip AD port direct acquisition
溫度測量電路電壓輸出範圍為0〜3.3V, PT1000 (PT1000電阻值發生了很大變化, and the temperature measurement sensitivity is higher than PT100; PT100更適合大規模溫度測量).

最簡單的方法是使用電壓分割方法. The voltage is generated by the TL431 voltage reference source chip, which is a 4V voltage reference source. Alternatively, REF3140 can be used to generate 4.096V as a reference source. Reference source chips also include REF3120, 3125, 3130, 3133, 和 3140. The chip uses a SOT-32 package and a 5V input voltage. 可以根據所需的參考電壓選擇輸出電壓. 當然, according to the normal voltage input range of the AD port of the microcontroller, 它不能超過3V/3.3V.

PT100 single chip AD port circuit direct acquisition

2.2 Resistor voltage division output 0~5V analog voltage, and the AD port of the microcontroller directly collects it.
當然, some circuits are powered by a 5V microcontroller, and the maximum operating current of the PT1000 is 0.5mA, so an appropriate resistance value must be used to ensure the normal operation of the component.
例如, the 3.3V in the voltage division schematic diagram above is replaced by 5V. The advantage of this is that the 5V voltage division is more sensitive than the 3.3V voltage, and the collection is more accurate. 記住, 理論計算的輸出電壓不能超過 +5V. 否則, the microcontroller will be damaged.

2.3 最常用的橋樑測量

The voltage divider circuit of PT100 outputs 0~5V analog voltage

Use R11, R12, R13 and Pt1000 to form a measurement bridge, 其中r11 = r13 = 10k, R12=1000R precision resistor. 當PT1000的電阻值不等於R12的電阻值, the bridge will output a mV level voltage difference signal. 該電壓差信號通過儀器放大器電路放大並輸出所需的電壓信號, which can be directly connected to the AD conversion chip or the AD port of the microcontroller.

該電路的電阻測量原理:

1) PT1000是熱敏電阻, and its resistance changes basically linearly with the change of temperature.

2) 在 0 度, PT1000的電阻為1KΩ, 然後UB和UA相等, 那是, uba = ub – 做= 0.
3) 假設在一定溫度下, PT1000的電阻為1.5kΩ, 那麼UB和UA不等. According to the voltage divider principle, we can find Uba = Ub – 做 > 0.
4) OP07是一個操作放大器, and its voltage amplification factor A depends on the external circuit, 其中a = r2/r1 = 17.5.
5) OP07 = UBA的輸出電壓UO * A. 因此，如果我們使用電壓表測量OP07的輸出電壓, 我們可以推斷UAB的價值. 由於UA是已知價值, 我們可以進一步計算UB的值. 然後, using the voltage divider principle, 我們可以計算PT1000的特定電阻值. 可以通過軟件計算來實現此過程.
6) 如果我們知道在任何溫度下PT1000的電阻值, we only need to look up the table according to the resistance value to know the current temperature.

2.4 恆定電流源
由於熱電阻的自加熱效果, it is necessary to ensure that the current flowing through the resistor is as small as possible, and generally the current is expected to be less than 10mA. 已經驗證了鉑電阻PT100的自加熱 1 mW will cause a temperature change of 0.02 to 0.75℃, so reducing the current of the platinum resistor PT100 can also reduce its temperature change. 然而, 如果電流太小, 它容易受到噪聲干擾, so it is generally taken at 0.5 到 2 毫安, 因此，將常數電流源電流選擇為1MA常數電流源.

The chip selected is the constant voltage source chip TL431, and then the current negative feedback is used to convert it into a constant current source. 電路顯示在圖中:

Constant current source of resistor PT100 circuit acquisition scheme

The operational amplifier CA3140 is used to improve the load capacity of the current source, 並且輸出電流的計算公式為:
Insert picture description here The resistor should be a 0.1% 精密電阻. 最終輸出電流為0.996mA, 那是, 準確性是 0.4%.
恆定電流源電路應具有以下特徵:
溫度穩定性: 由於我們的溫度測量環境為0-100℃, 當前源的輸出不應對溫度敏感. And TL431 has an extremely low temperature coefficient and low temperature drift.

良好的負載調節: 如果當前的漣漪太大, 會導致讀數錯誤. 根據理論分析. Since the input voltage varies between 100-138.5mV, 溫度測量範圍為0-100℃, 溫度測量精度為±1度攝氏, 因此，輸出電壓應每1升增加38.5/100 = 0.385mV. 為了確保當前波動不會影響準確性, 考慮最極端的情況, 在 100 攝氏度, PT100的電阻值應為138.5R. 那麼當前的漣漪應小於0.385/138.5 = 0.000278mA, 那是, the change in current during the load change should be less than 0.000278mA. 在實際模擬中, 當前的來源基本保持不變.

3. AD623採集電路解決方案
該原理可以指上上述橋樑測量原則.
低溫採集:

AD620 measures PT100 acquisition solution high temperature (150°)

高溫採集
Insert picture description here

4. AD620採集電路解決方案
AD620 PT100 acquisition solution for high temperature (150°):

AD620 measures PT100 acquisition solution at low temperature (-40°)

AD620 PT100 acquisition solution for low temperature (-40°):

AD620 measures PT100 acquisition scheme at room temperature (20°)

AD620 PT100 acquisition solution for room temperature (20°):

PT100 sensor high temperature acquisition circuit

5. Anti-interference filtering analysis of PT100 and PT1000 sensors
在某些複合物中的溫度獲取, 嚴酷或特殊環境將受到極大的干擾, 主要包括EMI和REI. 例如, 在應用運動溫度的應用中, high-frequency disturbances caused by motor control and high-speed rotation of the motor.

在航空和航空航天車輛內部還有大量的溫度控制場景, 哪個衡量和控制電源系統和環境控制系統. 溫度控制的核心是溫度測量. 由於熱敏電阻的電阻可以隨溫度線性變化, 使用鉑耐藥性測量溫度是一種有效的高精度測量方法. 主要問題如下:
1. 鉛線上的電阻很容易引入, 因此影響傳感器的測量精度;
2. In certain strong electromagnetic interference environments, the interference may be converted into DC output offset error after being rectified by the instrument amplifier, 影響測量精度.

5.1 航空航空公司PT1000採集電路
請參閱某個航空中的抗電磁干擾的空氣中PT1000採集電路的設計.

AD623 acquisition circuit scheme for PT100 sensor

在採集電路的最外端設置了一個過濾器. The PT1000 acquisition preprocessing circuit is suitable for anti-electromagnetic interference preprocessing of airborne electronic equipment interfaces; the specific circuit is:
通過電壓調節器將 +15V輸入電壓轉換為 +5V高精度電壓源. The +5V high-precision voltage source is directly connected to the resistor R1, and the other end of the resistor R1 is divided into two paths. One is connected to the in-phase input end of the op amp, and the other is connected to the PT1000 resistor A end through the T-type filter S1. OP放大器的輸出連接到反轉輸入以形成電壓跟隨器, 並且反轉輸入連接到電壓調節器的地面端口，以確保相一樣的輸入處的電壓始終為零. 通過S2過濾器後, PT1000電阻的一端A分為兩條路徑, one through resistor R4 as the differential voltage input D, 一個通過電阻R2到Agnd. 通過S3過濾器後, PT1000電阻器的另一端B分為兩個路徑, one through resistor R5 as the differential voltage input E, 一個通過電阻R3到Agnd. D和E通過電容器C3連接, D通過電容器C1連接到AGND, E通過電容器C2連接到AGND. The precise resistance value of PT1000 can be calculated by measuring the differential voltage across D and E.

通過電壓調節器將 +15V輸入電壓轉換為 +5V高精度電壓源. +5V直接連接到R1. R1的另一端分為兩條路徑, 一個連接到OP放大器的相位輸入, and the other connected to the A end of the PT1000 resistor through the T-type filter S1. OP放大器的輸出連接到反轉輸入以形成電壓跟隨器, 並且反轉輸入連接到電壓調節器的地面端口，以確保反轉輸入處的電壓始終為零. 此時, 流過R1的電流是常數0.5mA. 電壓調節器使用AD586TQ/883B, OP放大器使用OP467A.

通過S2過濾器後, PT1000電阻的一端A分為兩條路徑, 一個通過電阻R4作為差電壓輸入端D, 一個通過電阻R2到Agnd. 通過S3過濾器後, PT1000電阻器的另一端B分為兩個路徑, 一個通過電阻R5作為差電壓輸入端E, 一個通過電阻R3到Agnd. D和E通過電容器C3連接, D通過電容器C1連接到AGND, E通過電容器C2連接到AGND.
R4和R5的電阻為4.02K歐姆, R1和R2的電阻為1M歐姆, C1和C2的電容為1000pf, C3的電容為0.047UF. R4, R5, C1, C2, 和C3一起形成一個RFI過濾網絡. The RFI filter completes the low-pass filtering of the input signal, and the objects filtered out include the differential mode interference and common mode interference carried in the input differential signal. 在公式中顯示了在輸入信號中攜帶的公共模式乾擾和差分模式乾擾的計算:

航空航空公司PT1000採集電路

將電阻值代替計算, 通用模式截止頻率為40kHz, 差分模式截止頻率為2.6kHz.
終點B通過S4濾波器連接到AGND. 他們之中, 從S1到S4的過濾器接地端子都連接到飛機屏蔽地面. 由於流經PT1000的電流是已知的0.05mA, 可以通過測量D和E兩端的差分電壓來計算PT1000的確切電阻值.
S1至S4使用T型過濾器, 型號GTL2012X −103T801, with a cutoff frequency of M±20%. 該電路將低通濾波器引入外部接口線，並在差分電壓上執行RFI過濾. 作為PT1000的預處理電路, 它有效消除電磁和RFI輻射干擾, 這大大提高了收集值的可靠性. 另外, 電壓直接從PT1000電阻的兩端測量, 消除由鉛電阻引起的誤差並提高電阻值的準確性.