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Instant sensing of conveyed quantities

Ex lift truck with balance and radio data transmission
Instant sensing of conveyed quantities

The conveying system used at Haarmann & Reimer, a supplier of aromatic and scented substances, includes an operator-guided Ex lift truck equipped with a terminal, a bar code scanner, a weighing system and radio data transmission. The lift truck data is managed centrally on the terminal.

Dipl-Ing. Thilo Wenzel

In response to the increased demand for its products, H&R in Nördlingen is to construct a new, modern plant, designed in line with the latest state of the art. This plant is to be used specifically for making flavouring and improver substances for spirits. Since the alcohol here is not just a solvent, but also one of the principal ingredients of the end product, H&R’s entire production and storage area must be classified as „potentially explosive“. Suitably protected and approved components consequently have to be used for operation.
The concentrates for the numerous different flavours necessitate a complex mixing technique. All the individual substances must be transferred from their point of storage to the containers in which they are to be mixed according to a particular recipe. The majority of the substances can be supplied to the mixing area directly via a network of pipes. Essences that are required relatively infrequently and empty containers are kept in the storage area, from which they can be retrieved via the conveying system.
The latest available technologies will be used to optimize the production process. Central availability of all data – a prerequi-site of short response times – is a key feature, for example. The plant-wide concept, whereby all acquired information is accessible online on the central host, is also effective in the Ex area. Custom configurations are available for operator terminals and mobile systems with radio data transmission specifically for such areas. Depending on requirements, the terminals have either a graphics or a text-oriented display, varying numbers of function keys and either numerical or alphanumerical input techniques with the op-tion of radio data transmission. Ex storage batteries with various ratings are used for the mobile power supply.
The conveying system installed at H&R includes an operator-guided lift truck for on-line, recipe-controlled monitoring and weighing-in of the processed substances. This lift truck is equipped with a terminal, a bar code scanner, a weighing system and radio data transmission. H&R has opted for a graphics-capable display terminal with a number block and five function keys, which forms the interface between the operator and the host computer. The terminal is responsible for central management of the lift truck data. It has one main interface and two auxiliary interfaces for this purpose. The Ex-capable radio data transmission module, which sets up the online link, is connected at the main interface to the host computer. The operator acquires the data for the conveyed product using an intrinsically safe, hand-held scanner, which passes this information on to the terminal via one of the auxiliary interfaces. The strain gauge-based weighing system of the lift truck, which is likewise intrinsically safe, is connected to the second auxiliaryinterface. All the conveyed quantities can thus be sensed instantly.
Weighing technique
The central element is a lift truck with an integrated weighing system. The four weighing cells embedded in the fork are linked directly to a Termex 210 terminal via the Exawu electronic weighing components. The connection to the higher-level system is established at the host interface of this terminal by a radio data transmission module. The storage battery, which complies with the Ex-e type of protection, has a service life of approximately 18 hours – sufficient to guarantee continuous duty beyond a single shift. If multiple shifts are operated, a battery with a higher capacity or several interchangeable batteries can be used instead. In this case, the Ex-e battery must be disconnected from the lift truck by means of an Ex-de plug connector.
The balance can be calibrated for commissioning using the terminal setup program. The user is guided in a series of straightforward steps through the calibration routine, which is an integral part of this program. It is possible to specify the resolution (up to 6000d, default = 15 000d), the maximum weight, the unit and the linearization (linear, quadratic) of the balance.
The balance itself consists of the terminal, the electronic weighing components and the weighing cells. This balance can be calibrated and approved as a Class III device.
In stand-alone operation, the terminal also acts as a display unit with integrated taring and zeroing functions. The weight value is very easy to read if the terminal is set to the largest of the four available fonts. The terminal can moreover be rotated on the lift truck, so that the operator is able to read off the actual weight at any angle.
Radio data transmission
Radio modules are used to transmit the terminal data (of the scanners and balances) in the 460 MHz range. These modules communicate with the host computer via a central aerial. There are several central aerials which together cover the complete plant. Both Ex and non-Ex modules are available. The radio network in the safe area, which is allowed be operated with standard components, can thus be continued into the Ex area. This solution permits a standardized data acquisition concept to be implemented.
Application
Various frequencies and transmitting powers are available for radio data transmission. In the 460 MHz range, power up to 25 mW can be transmitted free of charge. Special permission to use the frequency must be applied for with higher outputs up to 500 mW. The advantage of transmitting with a higher power is that fewer central aerials are needed and that these can be erected farther apart. Transmitter outputs up to 25 W can be achieved in the 70 cm band, though only in the safe area and not in the Ex area.
In addition to mobile data entry devices in the safe area, mobile balances have to be operated in the Ex area. Central aerials are distributed around the hall for this purpose, so that the data sent by the mobile devices can be received at any point. The mobile devices merely pre-process the data, in order to facilitate fast, optimized radio transmission. The data which is received from these devices is edited and made available to the host computer on the data concentrator – the computer at which all the central aerials come together. In the opposite direction, the data concentrator receives data from the host, determines the destination address of the mobile device and sends the data to it via the nearest central aerial.
ExTec Oesterle
Fax: ++49/711/31545529
Further information cpp-200
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