Omega Products 44004 User Manual

Thermistor Elements

Thermistor bead shown actual size.

#32 tinned-copper wire 76.2 (3) L.

2.4 (0.095) diameter bead.

Dimension: mm (inch) Dimension: mm (inch)

76.2 (3)

Shown larger than actual size.

2.8 (0.11) diameter bead.

50.0 (2) minimum

76.2 (3)

PFA tube.

Thermistor bead with PFA sleeving shown actual size.

#32 tinned copper wire.

PFA tubing.

44000 Series

To determine the thermistor resistance at a specific

U Epoxy Coated Thermistor Beads U Precision Matched to 5 Standardized

Resistance Curves

U Maximum Working Temperature

75°C (165°F) or 150°C (300°F) (See Table Below)

U Available in Interchangeabilities

of ±0.1 or ±0.2°C (See Table Below)

Resistance Vs. Temperature Characteristics

The Steinhart-Hart Equation has become the generally accepted method for specifying the resistance vs. temperature characteristics for thermistors. The Steinhart-Hart equation for temperature as a function of resistance is as follows:

⁄T = A + B [Ln(R)] + C [Ln(R)]

where: A, B and C are constants derived from 3 temperature test points.

R = Thermistor’s resistance in Ω T = Temperature in degrees K

Table 1: Steinhart-Hart Constants Model Model

Number Number R25°C A B C 44004 44033 2252 1.468 x 10-3 2.383 x 10-4 1.007 x 10 44005 44030 3000 1.403 x 10-3 2.373 x 10-4 9.827 x 10 44007 44034 5000 1.285 x 10-3 2.362 x 10-4 9.285 x 10 44006 44031 10000 1.032 x 10-3 2.387 x 10-4 1.580 x 10 44008 44032 30000 9.376 x 10-4 2.208 x 10-4 1.276 x 10

temperature point, the following equation is used:

(beta-(alpha/2))1/3 – ((beta+(alpha/2))1/3

R = e where:

alpha = ((A-(1/T))/C) beta = SQRT(((B/(3C))3)+(alpha2/4)) T = Temperature in Kelvin (°C + 273.15)

The A, B and C constants for each of our thermistor selections can be found in Table 1. Using these constants with the above equations, you can determine the temperature of the thermistor based on its resistance, or determine a thermistor’s resistance at a particular temperature.

Typical Thermometric Drift (±0.2°C Elements)

Operating Temp 10 Months 100 Months

0°C <0.01°C <0.01°C 25°C <0.01°C 0.02°C 100°C 0.20°C 0.32°C 150°C 1.5°C Not recommended

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Tolerance Curves

Accuracy tolerances for thermistor sensors are expressed as a percentage of temperature. This is also referred to as interchangeability. We list two basic accuracy/interchangeability specifications for our thermistors, ±0.10°C and ±0.20°C from 0 to 70°C (32 to 158°F).

Table 2: Interchangeability Tolerances Model No. 44004 Model No. 44033

±0.20°C ±0.10°C

Temp

(°C) ±°C ±Ω ±°C ±Ω

-80 1.00 142,000 1.00 142,000

-40 0.40 2018 0.20 1009 0 0.20 75 0.10 38 40 0.20 10 0.10 4.9 70 0.20 2.7 0.10 1.4 100 0.30 1.3 0.15 0.7 150 1.00 0.9 1.00 0.9

Note: Temperature values (°C) are the same for each tolerance group (±0.10 or ±0.20), resistance tolerances will change based on resistance at 25°C (77°F).

Temperature vs. resistance tables for our thermistor products can be found on pages Z-236 and Z-237. The accuracy specification of ±0.1% or 0.2% means that each thermistor’s resistance will fall within these limits between 0 and 70°C (32 and 158°F). Table 2 illustrates the interchangeability values for the model numbers 44004 (±0.2°C) and 44033 (±0.1°C) at a number of temperatures.

Stability and Drift

While thermistors are generally very accurate and stable devices, conditions such as over-temperature exposure, humidity, mechanical damage or corrosion can cause uncontrolled changes in the resistance vs. temperature characteristics of the device. Once this characteristic has been altered, it cannot be re-established. This is one reason why most thermistors with a ±0.1°C interchangeability specifcation are rated for use at temperatures somewhat lower than those with an interchangeability of ±0.2°C.

Operating Current

The suggested operating current for bead-style thermistors is approximately 10 to 15 µA. Thermistors can experience self-heating effects if their operating currents are high enough to create more heat than can be dissipated from the thermistor under operating conditions. If higher operating currents are used, it is suggested that a self heating test be performed to insure the accuracy of the measurement.

Dissipation Constant

The dissipation constant is the power in milliwatts that will raise the resistance of a thermistor by 1°C (1.8°F) over its surrounding temperature. Typical values include 8 mW/°C in a stirred oil bath, or 1 mW/°C in still air.

Time Constant

The time constant is the time required for a thermistor to react to a step change in temperature. For example, if exposed to a change from 0 to 100°C (32 to 212°F), the 63% time constant would be the time required for the thermistor to indicate a resistance at 63°C (145°F). Typically, bare thermistors suspended by their leads in a well stirred oil bath will have a 63% response time of 1 second maximum. PFA encased thermistors exposed to changes in air temperature will typically have a 63% response time of 2.5 seconds maximum.

Discount Schedule

1 to 9 ...................................................................Net

10 to 24 ............................................................. 10%

25 to 49 ............................................................. 20%

50 to 99 ............................................................. 30%

100 and over ..................................................... 40%

To Order Visit omega.com/44000_thermis_elements for Pricing and Details

Resistance Storage and Working

Model @ 25°C Maximum Interchangeability Temp for Best Number (Ω) Working Temp @ 0 to 70°C Stability

44004 2252 150°C (300°F) ±0.2°C -80 to 120°C (-110 to 250°F)

44005 3000 150°C (300°F) ±0.2°C -80 to 120°C (-110 to 250°F) 44007 5000 150°C (300°F) ±0.2°C -80 to 120°C (-110 to 250°F) 44006 10,000 150°C (300°F) ±0.2°C -80 to 120°C (-110 to 250°F) 44008 30,000 150°C (300°F) ±0.2°C -80 to 120°C (-110 to 250°F)

44033 2252 75°C (165°F) ±0.1°C -80 to 75°C (-110 to 165°F) 44030 3000 75°C (165°F) ±0.1°C -80 to 75°C (-110 to 165°F) 44034 5000 75°C (165°F) ±0.1°C -80 to 75°C (-110 to 165°F) 44031 10,000 75°C (165°F) ±0.1°C -80 to 75°C (-110 to 165°F) 44032 30,000 75°C (165°F) ±0.1°C -80 to 75°C (-110 to 165°F)

Note: Thermistor elements are available with PFA sleeving over 1 lead wire and PFA overall, change middle digit model number to “1” for an additional cost to the base price for the ±0.2°C thermistors and add additional cost to the price of the ± 0.1°C thermistors.

Ordering Examples: 44004, 2252 Ω thermistor bead at 25°C, ±0.2°C interchangeability. 44033, 2252 Ω thermistor bead at 25°C, ±0.1°C interchangeability. 44104, 2252 Ω thermistor bead at 25°C, ±0.2°C interchangeability with PFA insulated lead wire and over-jacket. 44033, 2252 Ω thermistor bead at 25°C, ±0.1°C interchangeability with PFA insulated lead wire and over-jacket.

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