A thermistor is categorized by the total amount of resistance that is measured at ambient room temperature (25°C). There are specific technical specifications for devices that need their temperature maintained for optimal performance. Each manufacturer has different temperature sensing needs; therefore, it is essential to know about thermistor resistance and bias current. Knowing about these helps to determine optimum thermistor range.
Depending on bias current from controllers, a thermistor meets optimum useful range, which means that the temperature range in which small changes in temperature get accurately recorded. It is ideal to choose thermistors that have a set point temperature that is in the middle of the range you need. The sensitivity of thermistors depends on temperature. For instance, thermistors are known to be more sensitive at a cooler temperature as opposed to warmer temperatures.
Manufacturers specify the lower and upper voltage limits of the temperature sensor input of a temperature controller. You must select thermistors and bias current combinations that produce high voltage inside the range that is allowed by the temperature controller.
Voltage is understood in relation to its resistance by Ohm’s law. This equation is used because it helps to determine the bias current needed. Ohm’s law clearly states that currents through a conductor, between two points, is directly proportional to potential differences across both points.
When choosing a bias current and thermistor, it is crucial to decide on one where voltage developed in the middle of the range. Remember, controller feedback inputs should be in voltage (derived from thermistor resistance).
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