PT100和PT1000传感器探头温度采集电路

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.
Abstract generated by CSDN through intelligent technology

PT100/PT1000温度采集电路方案
1. Temperature resistance change table of PT100 and PT1000 sensors
镍等金属热电阻, copper and platinum resistors have a positive correlation with the change of temperature. 铂具有最稳定的物理和化学性质，用途最广泛. 常用铂电阻Pt100传感器探头的测温范围为-200～850℃, Pt500的温度测量范围, Pt1000 传感器探头, ETC. 都在陆续减少. 铂1000, 温度测量范围-200～420℃. 依据IEC751国际标准, 铂电阻Pt1000的温度特性满足以下要求:

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根据Pt1000温度特性曲线, the slope of the resistance characteristic curve changes slightly within the normal operating temperature range (如图 1). The approximate relationship between resistance and temperature can be obtained through linear fitting:

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1.1 PT100耐温变化表

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1.2 PT1000耐温变化表

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2. 常用采集电路方案

2. 1 Resistor voltage divider output 0~3.3V/3V analog voltage single chip AD port direct acquisition
测温电路电压输出范围为0~3.3V, PT1000 (PT1000阻值变化较大, and the temperature measurement sensitivity is higher than PT100; PT100更适合大范围温度测量).

最简单的方法就是采用分压法. The voltage is generated by the TL431 voltage reference source chip, which is a 4V voltage reference source. 或者, 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. 输出电压可根据需要的参考电压选择. 当然, according to the normal voltage input range of the AD port of the microcontroller, 不能超过3V/3.3V.

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2.2 Resistor voltage division output 0~5V analog voltage, and the AD port of the microcontroller directly collects it.
当然, 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. 记住, 理论计算输出电压不能超过+5V. 否则, the microcontroller will be damaged.

2.3 最常用的电桥测量

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Use R11, R12, R13 and Pt1000 to form a measurement bridge, 其中 R11=R13=10k, R12=1000R precision resistor. 当Pt1000的阻值不等于R12的阻值时, the bridge will output a mV level voltage difference signal. 该电压差信号经仪表放大器电路放大，输出所需的电压信号, which can be directly connected to the AD conversion chip or the AD port of the microcontroller.

该电路电阻测量原理:

1) PT1000是热敏电阻, and its resistance changes basically linearly with the change of temperature.

2) 在 0 度, PT1000的电阻为1kΩ, 那么 Ub 和 Ua 相等, 那是, 乌巴=乌布 – 做= 0.
3) 假设在一定温度下, PT1000的电阻为1.5kΩ, 那么 Ub 和 Ua 不相等. According to the voltage divider principle, we can find Uba = Ub – 做 > 0.
4) OP07是运算放大器, and its voltage amplification factor A depends on the external circuit, 其中 A = R2/R1 = 17.5.
5) OP07的输出电压Uo=Uba * A. 那么如果我们用电压表测量OP07的输出电压, 我们可以推断出Uab的值. 由于 Ua 是已知值, 我们可以进一步计算Ub的值. 然后, using the voltage divider principle, 我们可以计算出PT1000的比电阻值. 这个过程可以通过软件计算来实现.
6) 如果我们知道PT1000在任何温度下的电阻值, we only need to look up the table according to the resistance value to know the current temperature.

2.4 恒流源
由于热敏电阻的自热效应, 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. 经验证，铂电阻PT100自热 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, 如果电流太小, 容易受到噪声干扰, so it is generally taken at 0.5 到 2 嘛, 所以恒流源电流选择1mA恒流源.

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. 电路如图所示:
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The operational amplifier CA3140 is used to improve the load capacity of the current source, 输出电流的计算公式为:
Insert picture description here The resistor should be a 0.1% 精密电阻. 最终输出电流为0.996mA, 那是, 准确度是 0.4%.
恒流源电路应具有以下特点:
温度稳定性: 由于我们的测温环境是0-100℃, 电流源的输出不应对温度敏感. And TL431 has an extremely low temperature coefficient and low temperature drift.

良好的负载调节能力: 如果电流纹波太大, 会导致读取错误. 根据理论分析. Since the input voltage varies between 100-138.5mV, 温度测量范围0-100℃, 测温精度±1摄氏度, 因此环境温度每升高1℃，输出电压应变化38.5/100=0.385mV. 为了保证电流波动不影响精度, 考虑最极端的情况, 在 100 摄氏度, PT100的电阻值应为138.5R. 那么电流纹波应小于0.385/138.5=0.000278mA, 那是, the change in current during the load change should be less than 0.000278mA. 在实际模拟中, 目前来源基本不变.

3. AD623采集电路方案
原理可以参考上面电桥测量原理.
低温采集:
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高温采集
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4. AD620采集电路方案
AD620 PT100 acquisition solution for high temperature (150°):

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

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

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5. Anti-interference filtering analysis of PT100 and PT1000 sensors
一些复杂的温度采集, 恶劣或特殊的环境会受到很大的干扰, 主要包括EMI和REI. 例如, 在电机温度采集中的应用, high-frequency disturbances caused by motor control and high-speed rotation of the motor.

航空航天飞行器内部也存在大量的温控场景, 对电力系统和环境控制系统进行测量和控制. 温度控制的核心是温度测量. 由于热敏电阻的阻值可以随温度线性变化, 利用铂电阻测量温度是一种有效的高精度测温方法. 主要问题如下:
1. 引线上的电阻很容易引入, 从而影响传感器的测量精度;
2. In certain strong electromagnetic interference environments, the interference may be converted into DC output offset error after being rectified by the instrument amplifier, 影响测量精度.

5.1 航天机载PT1000采集电路
参考某航空某机载PT1000采集电路抗电磁干扰的设计.

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采集电路最外端设置滤波器. The PT1000 acquisition preprocessing circuit is suitable for anti-electromagnetic interference preprocessing of airborne electronic equipment interfaces; the specific circuit is:
+15V输入电压通过稳压器转换为+5V高精度电压源. 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. 运放的输出端连接到反相输入端，形成电压跟随器, 反相输入端连接稳压器的接地端，保证同相输入端电压始终为零. 经过S2过滤器后, PT1000电阻一端A分为两路, one through resistor R4 as the differential voltage input D, 并通过电阻 R2 至 AGND. 经过S3过滤器后, PT1000电阻的另一端B分为两路, one through resistor R5 as the differential voltage input E, 并通过电阻 R3 至 AGND. D和E通过电容C3连接, D通过电容C1连接到AGND, E通过电容C2连接到AGND. The precise resistance value of PT1000 can be calculated by measuring the differential voltage across D and E.

+15V输入电压通过稳压器转换为+5V高精度电压源. +5V直接连接到R1. R1的另一端分为两条路径, 一个连接到运算放大器的同相输入, and the other connected to the A end of the PT1000 resistor through the T-type filter S1. 运放的输出端连接到反相输入端，形成电压跟随器, 反相输入端与稳压器的地端相连，保证反相输入端电压始终为零. 此时, 流过R1的电流恒定为0.5mA. 稳压器采用AD586TQ/883B, 运放采用OP467A.

经过S2过滤器后, PT1000电阻一端A分为两路, 一、通过电阻R4作为差分电压输入端D, 并通过电阻 R2 至 AGND. 经过S3过滤器后, PT1000电阻的另一端B分为两路, 1.通过电阻R5作为差分电压输入端E, 并通过电阻 R3 至 AGND. D和E通过电容C3连接, D通过电容C1连接到AGND, E通过电容C2连接到AGND.
R4和R5的电阻为4.02k欧姆, R1和R2的电阻为1M欧姆, C1和C2的电容为1000pF, C3的电容为0.047uF. R4, R5, C1, C2, 和C3一起组成RFI过滤网络. 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. 输入信号中携带的共模干扰和差模干扰的‑3dB截止频率的计算公式如下：:

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将电阻值代入计算, 共模截止频率为40kHz, 差模截止频率为2.6KHZ.
端点B通过S4滤波器连接到AGND. 他们之中, 滤波器接地端子S1至S4均连接至飞行器屏蔽地. 由于流过 PT1000 的电流已知为 0.05mA, 通过测量D、E两端的差分电压即可计算出PT1000的精确电阻值.
S1至S4采用T型滤波器, 型号 GTL2012X-103T801, with a cutoff frequency of M±20%. 该电路在外部接口线上引入低通滤波器，并对差分电压进行RFI滤波. 作为PT1000的预处理电路, 有效消除电磁和RFI辐射干扰, 这大大提高了采集值的可靠性. 此外, 直接从PT1000电阻两端测量电压, 消除引线电阻带来的误差，提高阻值精度.

5.2 T型过滤器
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T型滤波器由两个电感和电容组成. 它的两端都有高阻抗, 插入损耗性能与π型滤波器相似, 但它不容易发生 “铃声” 并可用于开关电路.