1 / 9

Resistance Temperature Detectors (RTDs)

Resistance Temperature Detectors (RTDs). Characteristics and Applications. Characteristics: Resistive device, active, linear Large range: -200 to +850 o C for Platinum High accuracy: 0.001 o C Low sensitivity: 0.39 % per o C. Applications:

troy-baird
Télécharger la présentation

Resistance Temperature Detectors (RTDs)

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Resistance Temperature Detectors(RTDs) ISAT 300

  2. Characteristics and Applications • Characteristics: • Resistive device, active, linear • Large range: -200 to +850oC for Platinum • High accuracy: 0.001oC • Low sensitivity: 0.39 % per oC • Applications: • Industries and laboratories where high accuracy of temperature measurements are required. ISAT 300

  3. Thin-Film RTDs Thin-film RTD design is a newer technology and is gaining favor due to lower cost. It is designed to minimize strain on the platinum due to thermal expansion since strain also cause changes in resistance, R =(L/A). ISAT 300

  4. Calendar-Van Dusen Equation For platinum, the resistance temperature relationship is given by the Calendar-Van Dusen equation: For the U. S. calibration curve, a = 0.003921/°C ISAT 300

  5. Platinum RTD: R versus T(U.S. Calibration) ISAT 300

  6. R1 R2 Vout Vin R4 RRTD RTD’s Small Resistance Change • Bridge circuit: • Can detect small resistance changes • Adjust R3 so that R1/R4 = R2/RRTD More on bridge circuits next lecture! ISAT 300

  7. Circuits Used to Determine the Resistance of an RTD • Two-wire: Non-linear relationship between the measured votage and the RTD resistance. • Three-wire: Better results. • Four-wire: Resistance is a linear function of the measured volatge. ISAT 300

  8. Example: An RTD probe has a resistance of 100  at 0oC. The Calendar-Van Dusen constants are  = 0.00392,  = 1.49, and  = 0 for T > 0oC. What will be the resistance at 350oC. Alternatively, we could use table 9.3 and obtain RT = 231.89 . ISAT 300

  9. Summary • Thermocouples • Passive, non-linear, increase temperature increase voltages, big temperature range. • Types K and T are common devices. • Time Constant of a first order system • Thermistors • Active, highly non-linear, increase temperature decrease resistance. • Medical use, not available above 300oC. • RTD’s • Requires a Bridge, Linear by nature. • High accuracy, use in industry & laboratory. ISAT 300

More Related