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Linear Thermistor Components and Probes

Linear Thermistor Components and Probes
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Linear Thermistor Components and Probes - 1

Linear Thermistor Components and Probes Following is a description of why these networks produce linear information. The equation for a voltage divider network, consisting of R and R0 in series, is: R E out = E in R + R0 where Eout is the voltage drop across R. If R is a thermistor, and Eout is plotted versus temperature, the total curve will be essentially non-linear and of a general “S” shape, with linear or nearly linear portions near the ends and in the center. Figure 1A Thermistor Composite 44018 Figure 1B Thermistor Composite 44019 For applications requiring thermistors with linear response to temperature change, OMEGA offers linear components. These unique devices consist of a thermistor composite for temperature sensing and an external resistor composite for linearizing. Thermistor composites 44018 and 44019 each contain two thermistors packaged in a single sensor (Figures 1A & 1B). Thermistor composite 44020 contains three thermistors packaged in a single sensor (Figure 1C). Resistor composites for use with 44018 and 44019 thermistor composites consist of two metal film resistors of the size shown in Figure 2. Resistor composites for use with the 44020 thermistor composite consist of three of the same type metal film resistors. Linear components are manufactured with different values for different temperatures ranges. When they are connected in networks shown in Figures 3 and 4, they produce a varying voltage or resistance which is linear with temperature. One of the basic network manifestations is a voltage divider as in Figure 3A for components other than #44212, and as shown in Figure 3B for component #44212. The area within the dashed lines represents the thermistor composite. The network hookup for linear resistance versus temperature is shown in Figure 4A for linear components except #44212, and in Figure 4B for #44212. Linear Voltage vs. Temperature Linear Response Components Figure 1C Thermistor Composite 44020 Figure 2 Metal Film Resistor If R is modified by the addition of other thermistors and resistors, linearity of the center section of the curve, where sensitivity is greatest, can be extended to cover a wide range of temperatures. This section follows the general equation for a straight line, y = mx + b or in terms of a linear component: For Voltage Mode For Resistance Mode R t = MT + b E out = ±MT + b where M is slope where M is slope in volts / °T, in ohms / °T, T is temperature T is temperature in °C or °F, and in °C or °F, and b is the value of b is the value of the E out when T = 0° total network resistance, R t, in ohms when T = 0° Linear Resistance vs. Temperature R2 Note: Model 5830 precision benchtop thermometer includes linearized circuity, refer to section M. *RL1 may be any value as long as a new R1 value (R1A) is selected to satisfy the relationship:

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Linear Thermistor Components and Probes - 2

Sensitivity is 400 times greater than an IC thermocouple. Thermistor values as high as 30 mV/°C are common. In addition, output voltage can be applied to a recorder or digital voltmeter to produce a precise, sensitive, direct reading thermometer. Multiplexing The 44018 thermistor composite is used in four of the linear components. The part that changes in each component is the resistor composite, which determines the temperature range. Therefore, the 44018 thermistor composite can be used over the entire -30 to 100°C temperature range by simply changing resistor composites. Its accuracy and...

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Linear Thermistor Components and Probes - 3

Linear Components Kit Model No. Range Thermistor Composite Model No. Resistor Composite Model No. Resistor Composite Values Thermistor Accuracy & Interchangeability E0 Negative Slope Resistance Mode *Ein MAX. ***IT MAX. ***Load Resistance Minimum R.L. Linearity Deviation † Linear Components Kit Model No. Range Thermistor Composite Model No. Resistor Composite Model No. Resistor Composite Values Thermistor Accuracy & Interchangeability E0 Positive Slope Resistance Mode *Ein MAX. ***IT MAX. ***Load Resistance Minimum R.L. Linearity Deviation 44303 R1 = 18,700 Ω R2 = 35,250 Ω ±0.15°C ±0.27°F...

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Linear Thermistor Components and Probes - 4

Typical Linear Component Applications Ein Example 1: To measure and record on a 100 mV recorder temperature in the range 30 to 40°C. 1. Select Part number 44202 (temperature range -5°to +45°C) basic equation Eout1 = (-0.0056846 Ein) T +0.805858 Ein 2. Calculate Ein for 10°C equal to 100 mV (Eout, @30°C - Eout1 @ 40°C) = 100 mV [(-0.0056846 Ein) 30°C + 0.805858 Ein] - [(-0.0056846 Ein) 40°C + 0.805858 Ein] = 100 mV 0.056846 Ein = 100 mV Ein = 1.7591 Volts 3. Using the Linear network as two legs of a Wheatstone bridge add the two additional legs, R3 and R4 so that Eout2 = 0 when T = 30°C....

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Linear Thermistor Components and Probes - 5

Your One-Stop Source for Process Measurement and Control! UNITED STATES Deckenpfronn, Germany UNITED KINGDOM Manchester, England More than 100,000 Products Available! Calibrators, Connectors, General Test and Measurement Instruments, Handheld Instruments for Temperature Measurement, Ice Point References, Indicating Labels, Crayons, Cements and Lacquers, Infrared Temperature Measurement Instruments, Recorders, Relative Humidity Measurement Instruments, PT100 Probes, PT100 Elements, Temperature & Process Meters, Timers and Counters, Temperature and Process Controllers and Power Switching...

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