Safety in industrial processes is a valuable commodity. For this reason, mechatronic measuring instruments still experience strong demand. Operators use their output signals, for example, in the control room so they can collate and evaluate all the measuring results of a process. At the same time, an on-site display needing no external power is available as a fall-back. Thus, the process or the measuring point can be reliably monitored even if the power supply fails, and, if necessary, it can be manually controlled.
The electronic signal from the pressure or temperature measuring instrument is normally transported to the receiver via a cable. But it can also be ‘sent’ via telemetry. Remote data transfer is becoming more and more important against the backdrop of process efficiencies having to increase continuously. Manufacturing companies do everything they can to make optimum use of their machinery and avoid downtime. An operationally effective instrument for this can be the permanent tracking and monitoring of the relevant sensors and actuators in those processes adding value. If this information needs to be consolidated from decentralised, distributed processes or locations, an ideal solution is remote interrogation without cable – also known as telemetry.
The level measurement of liquid gas tanks is a prime example for the advantages of the combination of measurement technology and telemetry. These gases, such as argon, nitrogen, oxygen or carbon dioxide, which are required in many technical and medical applications, are nowadays often referred to as cryogens, and are stored in special tanks in a cryogenic, liquefied form.
The business model has changed
In the past, companies or end users of the gases kept a certain quantity in their own tanks and controlled the re-ordering themselves when required. For economic reasons, this process is increasingly being outsourced. The use of modern measurement technology has even allowed a change in the business model: The supplier or gas distributor not only ensures the supply, but also takes over the entire logistics. In addition to stock control, re-ordering and delivery, this also includes the provision of tanks including their maintenance. The customer merely enters into a leasing contract with the supplier.
In order to prevent gas bottlenecks for the consumer, the suppliers need an effective way of monitoring the stock of the individual, often nationally distributed tank plants. This model cannot be realised with ‘drive-by’ solutions alone, meaning the control is by employees on site. In order to be efficient and to calculate the logistics planning cost-effectively, the tank filling tailored to suit the requirements must be centrally controlled. The decisive parameters of level and working pressure must therefore be combined in a single data system. The exact detection of the two parameters is made difficult by the cryogenic ambient conditions: temperatures down to -200°C are present inside the tanks.
WIKA’s Cryo Gauge concept
WIKA has implemented the requirements resulting from this task in its Cryo Gauge concept. The compact and modular measuring assembly consists of three components: a mechatronic differential pressure gauge for monitoring the level, a mechanical working pressure indication with connected pressure transmitter, and a unit for remote data transfer. All components which are in contact with the medium are specifically designed for this measurement task. They are manufactured to oil and grease-free levels as standard and are therefore also suitable for oxygen use.
The core component of the measuring assembly is the mechatronic differential pressure gauge for monitoring the level, which can be derived from the differential pressure between liquid and gaseous phase in the tank. The internal design of the instrument is based on a special diaphragm, clamped by compression springs, which transfers the deflection in proportion to the pressure to a mechanical movement; the corresponding result is ultimately displayed on the dial. Taking account of the tank geometry and the density of the different gases, it is also possible to output information from the pressure measurement related to the contents, such as quantity and volume data, on the dial.
The second module is used to monitor, as required on safety grounds, the working pressure in the tank. If this increases as a result of temperature fluctuations or other external influences, in the worst case excess pressure and thus a correspondingly large amount of gas is discharged into the atmosphere via a safety valve. In order to be able to detect the potential product loss and the risk to the safety of the tank at an early stage, the working pressure is monitored with a mechanical indicator, i.e. a pressure gauge, and via the 4-20 mA signal of a mounted process transmitter.
The electrical outputs of the two measuring components form the input for the third module of the measuring assembly, the unit for remote data transfer (‘intelliMETRY’). The telemetry component digitises the analog measured values and transmits them via GSM technology to an online data centre. This can optionally be made using a GPRS or SMS mode. In principle, a permanent GPRS connection is preferred. The device determines whether this is possible from the network quality and, if necessary, switches automatically to the most stable network option. A built-in data logger collects and encrypts the data packets before transmission. In the event of any malfunction in the network, the data is buffered and transmitted with the next possible call.
In addition to the wireless connection, the instrument also has two cable outputs, which enable the measured values to be used locally. As a mechatronic system, the measuring instrument always provides the operator with a backup capability via the onsite display of the two measured pressure values, without any need for external power.
The wireless transmission of the data takes place at customer-specific intervals, in the case of tank plants generally hourly or daily. The intelliMETRY module also has additional monitoring functions. For example, in the case of an unexpectedly rapid dropping in the level, as a result of extraordinary consumption or leakage at the tank, a warning message is immediately triggered. The module also informs the operator about the completion of a filling operation.
All data from tank control passes to an online data centre. This is accessible through a password protected website, which can be accessed via browser or app. The incoming information is logged and visualised. The telemetry module can be configured and parameterised via the platform. This does not only apply to the data transmission mode and the monitoring functions. Users can set custom alarms and the type of notifications associated with them. It is also possible to integrate telemetry data into third-party systems or ERP software.
Conclusion
In addition to the level control of decentralised tank plants described here, the combination of traditional measuring technology and telemetry is also suitable for numerous other applications. In principle, any measuring instrument with an electrical output signal is suitable for this form of data transfer. The importance of such M2M systems is likely to continue to grow as a result of the pursuit of increasingly efficient processes and the development of new business areas within the framework of Industry 4.0.
| Tel: | +27 11 621 0000 |
| Email: | [email protected] |
| www: | www.wika.co.za |
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