‘Touchless’ two-part sensor helps bring in the harvest

The British manufactured Big Bale Transtacker provides an efficient, simple and effective method for collecting and stacking straw bales in the field as well as transporting bales to and from storage locations on the farm. The tractor towed machine collects and stacks its payload continuously as it is driven through the field with the operator controlling the entire machine from the tractor cab.

The Transtacker’s efficiency is largely due to the ‘auto pick up’ and the ‘auto tie’ functions that allow the machine to work seamlessly with minimal operator input. These functions work through a series of rotary sensors logging the position of the machine’s components and then relaying the data back to a control unit. Big Bale Transtacker’s Alex Baylis takes up the story:

“We had to reassess the Transtacker at the end of the 2012 harvest due to several reliability issues that were beyond our control. One of the issues encountered during the 2012 harvest was the reliability of the Hall effect sensor’ that we used. Not only were these expensive, they weren’t waterproof and also struggled with the precision that we were after. These issues meant that a lot of machines were experiencing problems and therefore weren’t operating efficiently, causing both the farmer and Big Bale Transtacker a lot of unnecessary problems.

“This is when we discovered the Novotechnik RFC4800 series angle sensors, specified and supplied by Variohm. The touchless technology sensor has answered all of these issues, with it offering very high levels of precision, being IP69K rated, and also very good value for money. Its two-part design has increased our confidence for much improved reliability – a very important factor for our equipment which is shipped world-wide.”

The two-part RFC4800 comprises an encapsulated magnet position marker that is attached to the rotating shaft and a physically separate sensor which is encased in a robust IP69 rated housing made from high-grade and temperature resistant plastic. With no mechanical coupling required, installation is very straightforward with generous alignment tolerances.

Without traditional bearing seals to wear, the sensor offers an effectively unlimited life for the mechanical parts and the 50,000 hour MTBF quoted figure for the electronics. The system provides a 12-bit resolution (0.09 degrees) analogue output which is absolute and therefore does not require recalibration after initial set-up or after complete power loss.

With its wide choice of supply voltages, output formats and electrical angle selection, the application flexibility available for the RFC4800 also allowed Big Bale Transtacker to match their requirements exactly, which had not been possible with the alternative methods that the company had considered.

With a prerequisite to operate the control system from 12 or 24V dc supplies, and provide a 4-20mA output, a standard option with a 9 to 34 V input capability was perfectly suited. Other standard supply options are 5 or 12Vdc with output options of 0-10Vdcas well as 0.5-4.5Vdc ratiometric. The RFC4800 was also supplied with a limited electrical angle. As standard, the unit has a 360 degree output with optional 30 degree increment version specials available as well as redundant output versions.

The Big Bale Transtacker is in use in many different countries and is designed to withstand the rigours of a variety of agricultural conditions. High shock and vibration as well as extreme variation in temperature and humidity are factored into the performance specification with reliability and the need to perform faultlessly being of utmost importance.

Variohm is no stranger to the agricultural machinery sector, for which it designs, specifies and supplies a wide range of position, load/force, pressure and temperature sensors.