Celsius (Fahrenheit) temperature frequency converter when the temperature range is offset

Celsius (Fahrenheit) temperature frequency converter when the temperature range is offset

AD537 has a linear temperature compensation characteristic, so it can be used to complete the temperature/frequency conversion function and serve as an interface for various temperature sensors. If the output signal of the sensor is to be used directly, the signal should be passed through a buffer first, because directly using AD537 as a load will seriously affect the output of the sensor and the voltage/frequency conversion circuit. By simply connecting with external resistors and capacitors, an absolute temperature/frequency converter can be directly obtained. When the temperature unit is not an absolute temperature, a reference voltage source is required for compensation. The connection method at this time is shown in Figure 3. Among them, the values ​​of each device when the temperature unit is Fahrenheit are given in parentheses. 

Before use, high-precision calibration should be performed. The following is an example of temperature in degrees Celsius. First, measure the room temperature in degrees K, and measure the output of pin 6 at this temperature. Second, adjust the offset according to the calculation. The calculation formula is: Offset voltage value (mV) = (6 pin) (mV) × 273.2/room temperature (K). Then, temporarily disconnect the 49Ω resistor, adjust the 2KΩ variable resistor to get the offset voltage at the specified node, and then connect the 49Ω resistor. Finally, adjust the 500Ω sliding variable resistor to get the appropriate frequency value at room temperature (25℃=250Hz). When the temperature unit is Fahrenheit, the calibration is similar to Celsius.