The 2006 FIFA World Cup was in full swing and fans all over the world enjoyed the matches on their private TVs and public large-format video screens. Reliable cooling systems were essential in the TV networks' outside broadcast (OB) units to ensure that both the equipment and the staff would keep working with maximum efficiency when things were getting hot, both inside and outside the stadia.
Until just a few years ago, interference and breaks in transmission were still quite common during the coverage of live events, but today's broadcasting technology is extremely reliable. One of the factors contributing to this improvement is the airconditioning that is now installed in the OB units.
These cooling systems are the speciality of Clim Cool Project in Renningen, Germany. The company has been developing airconditioning systems for special vehicles for over 10 years. One of their jobs was for a television OB unit installed in a large semi-articulated trailer truck, which was used throughout Germany during the 2006 World Cup. Packed with the very latest technology, the truck is reputedly one of the most advanced OB units currently available. It is designed to support up to 28 TV cameras and is already equipped for high-definition digital television (HDTV). In addition to the equipment it has space for a staff of around 18, including the audio technicians, video operators and broadcasting directors, all of whom work inside the trailer during the broadcasts.
To ensure that staff are comfortable and the equipment works reliably, Clim Cool Project fitted the trailer with a 70 kW airconditioning system for cooling, heating, ventilation and dehumidification.
Micro control system
The airconditioning has a total of 11 heat exchangers (one for each cooling station) and seven compressor units. The most important criteria for the selection of the components were low sound emissions and compact dimensions. Despite the trailer's dimensions - it is 5,7 m wide, 4 m high and 15 m long when it is set up for work - it is packed with equipment from floor to roof. Every last cubic centimetre of available space is used to the full and so the airconditioning components must also all be as small as possible.
The entire airconditioning system is controlled and monitored by seven Mitsubishi Alpha XL microcontrollers using 2-point control. The engineers at Clim Cool Project chose the Alpha XL because each unit supports up to 28 I/O points, eight of which can be used for analogue signals. These eight analogue inputs are needed to connect one Pt100 temperature sensor, a setpoint generator for each cooling station and two pressure transmitters for each compressor. The outdoor temperature is measured with an additional Pt100 sensor, from which the values are daisy-chained to all the controllers. The temperature values from the Pt100 sensors are converted into an analogue 0-10 V signal, which is then input to the controller.
The engineers also wanted to distribute the airconditioning control tasks across several smaller controllers to increase overall reliability. Should one of the controllers fail it would not stop the whole cooling system from working, nor result in the failure of the entire OB unit.
Another advantage of this system is that all the open and closed loop control processes are run in the controllers. This helps to keep the wiring and the number of terminals and hence space requirements to a minimum.
About the microcontroller
The Alpha XL microcontroller closes the gap between individual components like relays and time switches and a full PLC. It delivers a high level of functionality, reliability and flexibility at a reasonable price. Depending on the version it has between 6 and 28 I/O, eight of which can be used for analogue signals. The Alpha XL can process up to 200 function blocks in a single program and each function (such as time switches, counters, analogue signal processing, and clock/calendar function) can be used as often as required by all programs.
For more information contact Shaun Loesch, CBI-electric: low voltage, +27 (0)11 928 2000, [email protected], www.cbi-electric.com
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