Although, for most applications, the choice of sensor measuring principle or functional principle of the pressure sensor is not important, we are still often asked about how the sensor elements integrated in our pressure sensors and pressure transmitters work.

First of all, we would like to give a general definition:

Pressure sensors or pressure sensor elements are measuring elements which convert the physical quantity of pressure into an electrical quantity that is proportional to the pressure. Different physical effects and different sensor materials such as silicon, ceramic or metal are used.

WIKA uses industrial measurement’s 3 most common pressure-measuring principles, the instruments are developed in our own laboratories and also manufactured by ourselves:

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Due to the worldwide rising energy costs, the energy-efficient operation of refrigeration systems becomes a must. According to estimates, more than 90% of the refrigeration systems worldwide are not yet equipped with continuous control. They have been optimised and set for a certain operating state/refrigeration capacity – which means that they operate outside the optimum in all other operating states, whenever less capacity is required. This results in a waste of valuable energy.

In the future, systems without closed-loop control will no longer be acceptable. This is why manufacturers of refrigeration systems are increasingly using electronic pressure sensors, in order to control pressure and thus the resulting temperature of the refrigerant with high precision. The pressure sensors R-1 and AC-1 have been developed specifically for this use and in practice achieve substantial savings in electricity costs for the operators.

In practice, RoHS-compliant is often equated with “lead-free”. However, this is a widespread mistake. The RoHS directive 2002/95/EC aims to minimise the use of hazardous substances (including, among others, lead), but it does not completely exclude a small percentage.

One of the great obstacles in implementing the directive was the switchover to lead-free solder, because the limit values (0.1 per cent by weight of the inseparable components) do not admit a lead solder. This is probably the most important reason for the mix-up/equating that comes up again and again.

Unfortunately, we are asked too rarely regarding the specification of the IP68 rating for our pressure sensors and submersible pressure transmitters, i.e. how deep such an instrument may be submersed. However, this is not only a very meaningful question but also a mandatory one, because, contrary to almost all other IP ratings, the IP68 rating is only described and not fully specified by means of concrete values in the IEC 60529:

1. The first digit, the number “6″, means that the instrument has total dust ingress protection.
2. The second digit, the number “8″, means that the instrument is suitable for permanent submersion in water.

However, the maximum submersion depth of such an instrument is not specified. Thismakes total sense because there is a huge difference between submersing an instrument in a 1 m high water tank or using an instrument for measurements in a depth of 300 m on the ocean ground. According to the standard, the manufacturer and the user must therefore agree on the exact specification for IP68. Anyway, the IP68 rating must always be better than the IP67 rating, that means that the instrument may be submersed for at least 1 m.

In practice, it results in totally different immersion depths for our pressure transmitters and level probes depending on the area of application. The immersion depths range from 3 m to 300 m maximum. I.e. completely different submersion depths are specified for the same IP rating but depending on the application.

If you are looking for the suitable solution for your application, just ask your contact person for advice.

For more information please see our article “Definition of IP protection types“

Durable, robust and easy-to-read are the requirements for the display of industrial electronic pressure switches. State-of-the-art is typically a 4-digit 7-segment LED display in red. However, in particular the display of letters on the seven segments is only possible to a very limited extent and therefore these displays are often very difficult to read. However, letters are badly needed in order to make the parameters in the menu self-explanatory. The goal is setting the fundamental instrument functions, such as the units of pressure, as intuitively as possible, without having to read the operating instructions.

Since ten segments offer no real improvement for letters, a 14-segment display is the appropriate solution – with significantly better legibility of the parameters during setup. Make the comparison yourself …

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Manufacturers of electronic pressure switches often offer both PNP and NPN switching outputs. Here is a brief explanation how the two different outputs should be connected. In principle, both are bipolar transistors in which only the internal arrangement of the pn transitions differs. This is why the load must be connected differently to the transistor outputs.

PNP switching output:
The load is connected to the switching output with GND as the reference point. When a change in signal takes place by reaching a pressure value, the supply voltage (+Ub) is “switched through”, allowing current to flow from +Ub through the transistor and through the load to GND.

Equivalent circuit diagram and wiring of pnp transistor switching output

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In connection with the electronic pressure switch PSD-30, I often get asked what is IO-Link and how it is defined. IO-Link is a new communication interface in the area of factory automation/ machine building. Leading providers of automation technology have joined together to form the “IOLink consortium” and specified this new interface. This interface can be used to exchange information on the already existing signal line all the way down to the field level, using a serial protocol. The advantage is that, for example in the case of a pressure switch, bidirectional communication is possible via the already existing 3-wire connection. The following data can be exchanged using the standardised protocol:

• Measurement values: analogue or digital
• Configuration parameters: centrally from the control system to the sensor/actuator
• Diagnostic information: from the instrument to the control system

For further details on IO-Link, please refer to the IO-Link homepage or the product page for the WIKA PSD-30 electronic pressure switch.

The main reason for using a pressure sensor with CANopen interface compared to customary analogue sensors is the low degree of wiring required and the high reliability of signal transmission.

The data and power cables of the CAN bus are combined in a single shielded CAN cable and passed on from one bus user to the next, i.e., the bus is really a “chain” of CAN bus users. As a result, each bus user must be provided with two electrical connectors- an input and an output. For sensors in the industrial environment, the connector most widely used for this purpose is the M12x1 connector.

The electrical connection of the device is made either via an external T-piece (see picture on the right) or via Y-connectors directly integrated into the sensor (see picture on the left)

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The recovery of drinking water from ground water has top priority in many countries. In Germany, this method has a share of about 70 per cent in the water supply. The water drawn from depths of several hundred of meters below the earth’s surface is normally in perfect hygienic condition.

The ground water is pumped up to the surface by means of powerful submersible pumps. The ratio between the water removal and the replenishment of the ground water must be permanently monitored. Submersible pressure transmitters which continuously measure the water level are used for this purpose. This application requires special low-maintenance and very durable instruments. The WIKA submersible pressure transmitters can be submerged completely and operated permanently under water. They are reliable instruments that deliver value for many years.

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The response time of pressure sensors is reflected in a large number of varying parameters, such as the response time, settling time or rise time in specifications or data sheets. In general, it can be assumed that the response time is defined as the interval required by the output signal of a pressure sensor  to display a change in the applied pressure. Of greatest practical relevance is the so-called rise time.

The graphic shows a simplified diagram of a steplike change in pressure (shown in blue) with a time-delayed change in signal of the pressure sensor (shown in red).

For the sake of simplicity, the picture only shows an ideal situation. In reality, the response time of pressure sensors contains further influencing factors, such as dead time or overshoot, due to their particular constructive setups.

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