Controlled valves ensure correct motion

Modern valves need to be precisely controlled. Even the uncontrolled movement of the control spool in a valve by a few micrometres can cause damage to a system. Consequently, it is necessary to monitor the movement of the spool.
Together with a well-known German manufacturer of such valves, the sensor technology company, Micro-Epsilon, has developed an innovative solution for the measurement of the spool movement and gained this manufacturer as an OEM customer.

The spool in a valve controls the oil flow to the hydraulic cylinder. When the spool moves to and fro, the drill-holes in the body of the valve open and close. To achieve this, the spool is driven by a linear motor.

For this measurement the sensor induNCDT series LVDT from Micro-Epsilon is used. The sensor is mounted on a pressure line located on the valve. In this pressure line a freely moving plunger is guided, which is permanently fixed to the spool. The sensor acquires the plunger through the metal of the pressure line and in this way determines the exact position of the spool. The plunger forms a passive position transmitter having a number of advantages. The measurement occurs without contact and is not subject to pressure, because the sensor is mounted outside of the pressurised region. This means that the sensor can be produced from inexpensive polymer plastic, keeping the price for the sensor very low.

This sensor is now included on many models in the valve series. By using it, the manufacturer offers an exactly controlled flow of hydraulic oil into his products.
For the sensor, there is a miniaturised electronic system from the sensor manufacturer, which can be implemented in any existing valve control. The ISC700 consists of an analogue sensor ASIC for the evaluation of the sensor signals and a freely selectable microcontroller for the computation and conditioning of the measurement data.

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