Hygienic measurement of all aspects of temperature and pressure

In the food and pharmaceutical industries, hygienic measurement of pressure and temperature is becoming increasingly important in data acquisition, with increasing quality requirements. At the same time, a large number of proven and reliable probes and transmitters are entering the market.

People often measure pressure and temperature in gases, liquids and viscous media, which is not only related to the product medium itself, but also the necessary process medium and cleaning media, such as steam, detergents, etc. The requirements for measuring points in different applications are also diverse.

Nowadays, CIP equipment is used in many fields for automatic cleaning, and sensors The design of process connections must also enable product residues, microorganisms and other residues in the connections and channels to be completely removed by cleaning agents and disinfectants. In industry, a variety of process connections without dead ends have been developed accordingly.

New, more flexible adapter systems

Some equipment manufacturers have to use a relatively large number of process connection systems in order to optimally meet the requirements of different end users. As an alternative to the usual fixed welded process connections, a universal adapter system has been developed, which is called PEKA. This system relieves the equipment manufacturer from the need to select and stock transmitters that are not related to the process connection. They can be quickly and freely installed at any time, which also reduces inventory costs and shortens delivery time.

For pressure sensors, piezoresistive or ceramic capacitive sensor elements are often used. Similar to temperature probes, the use of piezoresistive sensor elements ensures that all process contact parts are composed of stainless steel. The sensor element is an oil-filled system, and the oil filled can also be replaced with a filling oil similar to food oil. This ensures that the entire batch of products will not be wasted in the event of a sensor element failure. Needless to say, there are many FDA-compliant filling oils available on the market.

It is also possible to use sensor elements without filling oil. The sensor surface is made of ceramic (Al2O3) and the connection requires a seal. The commonly used seals are made of FKM or PTFE. Since the contact part uses ceramic/seal/stainless steel, the process connection dead angle structure is not as good as the piezoresistive element in this case.

Pt thermal resistor ensures application

For temperature acquisition and processing, Pt thermal resistor (Pt100, Pt500 or Pt1000) has corresponding outstanding characteristics. The advantage is the high compatibility and good repeatability of its electronic characteristics. The standard DIN EN60751 has the corresponding relationship between resistance and allowable deviation and temperature, so it can be replaced at any time. The

maximum boundary deviation corresponding to temperature is defined as tolerance class A and class B in the DIN standard. In the food and pharmaceutical industry, high-precision probe class A is used.

For the necessary electronic components, high-quality stainless steel junction boxes are used as required, with a protection level of IP67. It is also possible to install 1 or 2 measuring loops in a 3-wire system according to the measurement task. Thermal resistors are usually suitable for 50℃～250℃ in this structural form.

For longer transmission distances, thermal resistors use transmitters to convert resistance values ​​into standard signals. In most cases, analog output transmitters are used. Its temperature linear outputs are 0mA~20mA, 4mA~20mA and 0 V~10V.

The manufacturer's new products should meet the industry's high standards and necessary integration characteristics. The thermal resistor transmitter Dtrans T100 is fixedly integrated in a very small cylindrical terminal. The measurement range and the necessary or optimized parameters for operation can be configured through an installation program. The output signal has 4mA~20mA or vice versa 20mA~4mA temperature linearity to choose from. The high-temperature protection tube model can measure up to 260℃, and the standard unprotected tube model is applicable to -50℃~200℃. The thermal resistor has an EHEDG certificate and is very suitable for the food and pharmaceutical industries.

Compared with temperature measuring instruments, modern pressure measuring instruments are always integrated with sensors and transmitters, thus meeting the commonly used measuring ranges from 0mbar to 100mbar to 0bar to 25bar. The permissible medium temperature can be from -30℃ to 120℃ under standard conditions. For CIP equipment and sterilization processes, hygienic process connections that can reach a medium temperature of 200℃ are also available.

The accuracy of the pressure transmitter can theoretically be determined by linearity and temperature influence. Its values ​​are different for analog output and digital output. The linearity is ≤0.2%~1.0% for analog signals and ≤0.1% for digital signals. The typical temperature influence is 0.02%/K for analog signals and 0.005%/K for digital signals. For electrical connections, different solutions are available depending on the protection level. For IP65, a junction box according to DIN EN 175301 is sufficient. For IP67, a fixed cable or M12 round connector should be used.

For users
* In the food and pharmaceutical industries, it is very important to choose the right temperature and pressure sensors in order to produce products of the same high quality.

* From a technical point of view, all measurement tasks can now be solved.

* In order to meet the high standards and requirements of the food and pharmaceutical industries, equipment manufacturers need corresponding qualification certification systems, such as EHEDG or FDA.

* When choosing an instrument, other aspects should also be considered, such as price and service life.

Trend: Digitalization

Many devices controlled by PLC or industrial computers use digital buses for signal transmission. In this way, the measurement output signal cannot be a standard analog signal, but must be a digital signal that can be directly input into the bus system. In order to meet this requirement, a transmitter with CANopen interface was developed, which reduced the number of connecting cables from the analog instrument to the control cabinet. A greater price advantage is the saving of analog I/O modules in the control cabinet, that is, analog control inputs. In addition to direct cost savings, users can also enjoy other advantages, such as the decentralized intelligent function of digital sensors, which makes the entire automatic control system simpler. Digital sensors and digital signal transmission also offer protection over analog systems in the event of erroneous measured values ​​(due to electromagnetic interference) or unexpected system interruptions. And this is not the last advantage, there are many more…