IGBT模塊NTC溫度傳感器阻值與溫度測量

1.采用模擬電路方式測量IGBT模塊NTC溫度傳感器溫度：
這個基本的方法是基于一個分壓器作為熱敏裝置，如下圖所示： NTC的特性在數(shù)據(jù)手冊中有兩種不同的格式，一種圖形方式R=f(θ)，該函數(shù)可近似解析描述該圖形的全部參數(shù)。有效的數(shù)學(xué)表達(dá)式如下： 為了更精確地計(jì)算，如果集中在一個較小的溫度范圍，規(guī)格書也提供了B25/50及B25/80的值。文章來源：http://www.oldschoolsausage.com/sr/162.html
根據(jù)已知測量的UR，實(shí)際電阻R(θ)的值可由下式計(jì)算： 如果有一個溫度期待值，該方程可以很容易地通過微處理器處理，采用數(shù)字化的UR作為輸入。
如果只是需要一個最高溫度作為閾值信號，采用一個比較器觸發(fā)預(yù)定值就足夠了。
分壓器電阻R1的規(guī)定：
Choosing R1 needs to be done carefully to achieve a proper reading. If chosen too small, the flowing current inside the NTC will lead to losses that in turn heat up the device thereby falsifying the measured results. If, on the other hand, R1 is chosen too large, the measured voltage gets too small and in turn the measurement looses accuracy again.
To minimize the influence of the current, a thermal view is helpful. The thermal conductivity for the NTC is 145K/W. If a 1K influence is tolerable, the power dissipation inside the NTC may not exceed Pmax=6.9mW.
Assuming that a measurement up to 100°C needs to be done, the NTC will reach a value of R100=493. From this, the maximum current can be calculated to be With a supply voltage U1=5V and a current limit of 3mA, the resistor R1 becomes As there is no such resistor, 910can be chosen, leading to Imax=3.56mA; any value that limits the current to I<4mA can be considered as long as 1K difference is tolerable.
2.采用數(shù)字方式測量IGBT模塊NTC溫度傳感器溫度：
除了用一個電壓分壓器，NTC電阻隨溫度的變化可用來影響一個RC網(wǎng)絡(luò)的時間常數(shù)，如下圖所示： Figure 7 Basic schematic to get a digital temperature information
電阻R11、R12決定了比較器改變輸出狀態(tài)的閾值，輸出信號電壓Uout被用來觸發(fā)晶體管Q1以使電容器放電。電容通過NTC電阻R(θ)充電，Uout以一定的頻率fout=g(θ)工作在脈沖模式。
為了根據(jù)Uout重建實(shí)際溫度，采用一個規(guī)定的時間段內(nèi)的脈沖計(jì)數(shù)是足夠的。脈沖數(shù)代表了溫度值，脈沖數(shù)與溫度的映射可以通過解析描述或者兩個最接近的值之間的插值查表。