Thermistor with Wheatstone bridge
What is Thermistor?
Thermistors are thermal resistors. Their resistance is temperature-dependent.
They are mostly characterized by their resistance and B value (fixed material constant describing the shape of the resistive slope). Because the relationship between resistor and temperature is non-linear, NTC thermistors are widely used (non-linear decrease).
They are highly compatible and versatile (can be customized and fabricated into many forms).
Steinhart Equation models the thermistor’s resistance at different temperatures. One benefit it has is it provides a more accurate calculation of the thermistor’s temperature than other equations.
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Characteristics of Thermistor
Output
Resistance (Ω)
Range
-30 up to +130 °C
Relationship
Non-linear
As temperature increases, its resistance decreases
Pros
Cheap
Large change in (Ω)
Cons
Non-Linear
Small Range
Voltage Dividers
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Voltage Dividers are circuits which turn large voltages into smaller voltages.
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Voltage Divider creates an output voltage which is a fraction of the input voltage by distributing the input voltages across its components.
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By just using two resistors, a significant proportion of any input voltage can be dropped across each one. It uses the same principles as Ohm's law to evenly distribute its voltages.
Wheatstone Bridge
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Wheatstone bridge is a widely used method of accurately measuring resistance of a circuit. It is widely configured in a "diamond" form, consisting of four resistors and a voltage across the ends of the diamond configuration.
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We want to find the resistance values of Rth, R2, R3, and R4 of the Wheatstone bridge. We also want to find Voltage in the bridge.
Wheatstone bridge Calculator
Use this calculator, to find the resistance values based on your temperature range:
Differential Amplifier
In this part, we are connecting the Wheatstone bridge with a differential amplifier. First, we need to calculate Thevenin resistance and Voltage out of the bridge.
In order to do that, the following calculator is generated. Enter resistance values and Vs and click go to do the calculations.
Finally, we want to calculate the voltage in the differential amplifier.