Thursday, July 30, 2015

Testing access barriers.

Yokogawa’s PX8000 Precision Power Scope is playing a key part in production tests being carried out by Magnetic Autocontrol Group of Schopfheim, (D): a major global supplier of vehicle and pedestrian access barriers for installations as diverse as access barriers at Frankfurt Airport, the Paris Metro ticket control systems and the Kuala Lumpur Petronas Twin Towers.
Each year, Magnetic Autocontrol produces more than 15,000 barriers for the world market. The products are based on a modular system using a range of standard components which can easily be customised according to user requirements. For orders from outside Germany, often only subassemblies or components are shipped from the factory at Schopfheim. These are then further processed and assembled by the company’s global branches to produce the finished end products. This process significantly reduces the transport and storage costs resulting in increased efficiency in the overseas sales activities.

In principle, the operation of these barriers is similar to the direct drive of a 3-phase control system. The heart of the system consists of one or more motors along with a control unit. Depending on the application and customer requirements, different interfaces are selected including USB, RS485 or Ethernet Ports as well as inputs from card readers, key switches or loop detectors. The number of drives can vary, from one for a standard barrier, up to four for a pedestrian gate.

The latest products use a direct drive with 3-phase control using pulse width modulation of an internal supply voltage of 24 V DC. The power supply has a wide input range from 85 to 264 V at 50 to 60 Hz, allowing it to be used worldwide. The direct drive used and its integrated control electronics are characterised by high torque at low speed and ensure very short opening and closing times, sometimes even less than a second.

During this short period, high current normally flows. However, in standby mode the power consumption should be as low as possible in order to minimise operational costs. This means that, for a typical pedestrian gate, the power consumption can change within seconds from a few milliwatts to around 10 watts: about a factor of 1000.

There are three different operating modes: standby, holding and rotating, and the performance in all three modes needs to be measured accurately. In order to achieve high-accuracy measurement, Magnetic Autocontrol places great emphasis on choosing the right technology and the right product.

For more than 10 years, Magnetic Autocontrol has used Yokogawa’s PZ4000 power analyser for verification of the drives’ performance: specifically to measure the current and power to help in understanding the performance of the barriers. The evaluation includes measuring the actual power consumption in standby mode and during operation and comparing it with the values in the product specification and the operating instructions. These data are required in order to determine the overall operating cost as well as to analyse the effectiveness of the electrical connections.

“Although the theoretical values ​​for the specifications and manuals can be calculated, we still have to verify the results in the form of a type test”, says Andreas Scherer, Manager of Testing at Magnetic Autocontrol: “With our latest generation of barriers, we estimate that one employee was tied up in these measurements for around two months.”

Measurements are typically taken on various barrier configurations with mains voltages between 120 V and 230 V and with boom lengths from 3 to 10 m in increments of 50 cm.

Last year, the PZ4000 power analyser was replaced by Yokogawa’s latest PX8000 Precision Power Scope. This is an ideal instrument for capturing short current spikes, especially in today’s direct drives. The PX8000 has three current/voltage inputs and a module which can be connected to an external sensor. This means that other related operations such as the opening angle of the barrier can be recorded in parallel. It is also possible to directly measure the power usage on the three phases on the motor or the primary side to accurately obtain the total power consumption.

“The Yokogawa PX8000 is a big help to us in our problem analysis”, says Andreas Scherer: “In order to examine specific details, we had previously always used an additional oscilloscope with current clamps to get all the measurements we needed. With the new PX8000, we can now accurately measure everything with a single device.”

Other benefits of the Precision Power Scope include its much higher (12-bit) resolution and the history memory function for evaluating tests retrospectively. “We can now re-visit past test results without the need to build the whole experimental set-up again. For us this is a quantum leap.”

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