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TD temperature transmitters

Technology overview

ifm uses a highly engineered construction method. The RTD element is first bonded to a thin film carrier. This reduces the thermal mass of the electrical leads. The film carrier and RTD element is then attached to a specialized assembly carrier. The carrier positions the RTD element into precisely the correct location and preloads the RTD with constant force against the probe’s inner sheath wall. This allows the RTD element direct and constant controlled contact to the sheath, minimizing the amount of thermal mass separating the RTD element from the process media. The result – fast and repeatable response!

Ordinary RTDs and temperature instruments have the sensing element potted into the tip of the sheath tube. The potting compound acts like an insulator, slowing the heat transfer to the RTD element. Typically, the RTD element location is not controlled, but simply lowered by its lead wires into the sheath and glued into place. Both of these factors lead to poor uniformity, repeatability and response time.

Applications

CIP Skids

Monitoring the temperature of fluids used in a Clean-in-Place system is vital to ensure the entire system is sanitized. What if you could reduce inaccuracies of your measurement system and improve signal durability while reducing your overall system cost?

Traditional sensors are prone to moisture ingress, require costly calibration, and have no display for local indication. The 3A authorized one-piece construction of the TD offers the highest level of integrity in sanitary applications and makes it ideal for use on a CIP skid.

Heat Exchanger

Heat exchanger fluid temperatures are critical measurements in process applications. What if you could eliminate the primary issues associated with temperature instrument drift?

The integrated RTD element, LED display and one-piece design eliminates ingress which is the primary contributor to instrument drift.

Unlock sensor potential with IO-Link

Via IO-Link, the TD family can provide:

  • Process temperature transmitted digitally without A/D and D/A conversion losses
  • Sensor diagnostics
  • Remote parameterization

FAQs

Q. How is response time for a temperature instrument specified?

A. “T05” and “T09” refer to the reaction time in seconds for the sensor to measure a change in temperature, typically 0…100 °C. T05 and T09 are the times the measurement take to reach 50% and 90% of the temperature change.

Response time as shown on our datasheets are for instruments directly inserted into the process using water as the medium. If thermowells are used, the response time will be affected. Heat transfer grease can be used inside the thermowell to improve the response time.

Q. Why would I use a thermowell in an application?

A. Thermowells provide:

  • Ease of instrument inspection without opening the process system.
  • Higher pressure rating than probe alone.
  • Resistance to high flow, viscosity, and abrasive media.

Matching thermowells can be found on the Accessories tab of the instrument's datasheet.

Q. What is the advantage of an integrated display on the instrument?

A. The value displayed is the actual process temperature and it is unaffected by programming or scaling. It provides a reference value to confirm correct system configuration.

Q. The TD sensors do not have pushbuttons.  How do I change the measuring scale?

A. LR Device (QA0011) is ifm’s software to configure sensors. It can be used with a USB cable (E30390) connected to a laptop. Sensors can also be configured remotely using IO-Link.

Q. How do I calculate the accuracy of the TD sensors?

A. Since the TD is a one-piece design and calibrated at the factory as the complete system, calculating the accuracy is a simple equation. The datasheet calls out: 

                                        ± 0.3 + (± 0.1% Measuring Span) °C

For example, a TD scaled for 0…100 °C has an accuracy of:

                                        ± 0.3 + (± 0.001 x 100) = ± 0.4 °C

Q. ifm’s temperature instruments use RTDs. What is the difference between an RTD and a thermocouple?

A. RTDs (Resistance Temperature Detector) change a very predictable amount of resistance for every degree change in temperature. ifm offers both Platinum (Pt) 100 and Platinum (Pt) 1000 RTDs. Pt100 devices change 0.385 ohms per °C and Pt1000 devices change 3.86 ohms per °C. RTDs are capable of measuring into the 600 – 700 °C range, and they provide an absolute measure of temperature. They are stable over a long period and are generally more accurate than thermocouples. RTDs use standard instrument cabling and do not need exotic alloy thermocouple wire. The overall total cost of ownership for RTDs is less than an installed thermocouple system.

A thermocouple consists of two dissimilar exotic metals joined together. The joined contact point produces a sensitive millivolt signal that varies as a function of temperature. Thermocouples are capable of high temperature measurement (1500+ °C), but only provide a relative temperature difference between the tip and leads. Thermocouple wire is required to connect them, and they can be sensitive to electromagnetic noise.