Fieldbus solutions are being increasingly used worldwide in the process industry. The fieldbus market promises, according to high profile studies, a clear growth over the next few years.

To be represented on a broad front in this market the existing FOUNDATION Fieldbus™ transmitter portfolio which includes the products:

-iTEMP® TMT162 FF with 2 sensor inputs and the
-iTEMP® TMT125 multi-channel with 8 sensor inputs

Connection Technology

The iTEMP® TMT85 head transmitter has 2 sensor inputs for resistance thermometers, thermocouples, voltage and resistance transmitters. These sensors can be connected in a lot of different varieties, like for example 2xPt100/3-wire. This is not possible on competitive products with only 4 terminal clamps. Furthermore two different types of connection technology can be selected on the TMT85. One is the novel spring-loaded clamp technology. Thereby fixed as well as flexible conductors with core cable ends can be inserted directly without any tool. This connection method has the huge advantage that the wiring time is shortened and a permanently safe contact between conductor and clamp exists. Thus a loosening of the screws or corrosion on the clamping points is not possible. The alternative to this novel version are the well-known screw terminals with gold plated contacts, which hold conductors with core cable ends with a diameter of up to 2.5mm2.


Safety

The trend towards increased safety in the process is supported by a multitude of functions on the iTEMP® TMT85. Detection of open circuit as well as short circuit and incorrect connection are as natural a part of the transmitter just as corrosion detection on the sensor cabling on RTD 4-wire connection or thermocouples. Thereby the circuit resistance between the sensor and the transmitter is monitored continuously. In the case of an unbalance between the individual conductors a warning or an alarm is transferred to the control system.

On 2-channel-operation further safety relevant functions like for example a backup function and sensor drift recognition are available.

With the help of the backup function an increased availability of the measurement point can be realized, since, in case of a failure of the primary sensor, the backup sensor continues the measurement without interruption so that the operation is continued non-stop.

At drift recognition the both redundant sensors are constantly compared. If on one of the sensors there is a drift due to mechanical or thermal overstraining that is above the preset value, a message is sent to the control system. Hereupon the measurement point can be checked and the defective sensor can be replaced.


Accuracy

The accuracy of a thermometer plays a decisive role in many processes. For significant improvement in the temperature measurement accuracy a sensor-transmitter-matching process can be carried out on the iTEMP® TMT85. This can be done sensor specifically with two different methods:

-Linearization with the Callendar-Van-Dusen-Coefficients for Pt100 resistance thermometers
-Linearization with a polynomial for copper / nickel resistance thermometers

In both cases the specific coefficients from the sensor calibration can be entered into the iTEMP® TMT85 thereby getting higher accuracy of the complete measurement point. The higher accuracy results from the fact that the transmitter uses the specific data of the connected sensor instead of the standardized sensor curve data for the calculation of the measured temperature.


Conclusion

Due to its practice-related functionalities the iTEMP® TMT85 features a maximum on safety in the process and the possibility to improve the entire measurement point in regard to accuracy. This device is a further step towards the "hot formula” E+H = °F

Courtesy of  Endress Hauser