I to H converter (from Voith) , also called as “current to hydraulic pressure” converter or I/H Transducer or Electro-Hydraulic converter, converts an electronic signal (analog output), typically from a control system such as PLC or DCS, to a hydraulic signal used to control hydraulic piston cylinder that actuates the control valve. This signal from the control system is typically analog signals in the range of 4mA to 20mA loop (or of other range of electric signal too). Since hydraulic actuators are operated under high hydraulic pressure up to a range of 6000 PSI. So I/H converter can be used either directly for low hydraulic pressure or provide a control operation as pilot signal that operate pilot relay/ pilot valve connected to hydraulic circuit. A typical I/H Converter is shown below-
Principle of operation-
To understand the working of I/H Converter, we should know about the parts of a I/H converter as mentioned below-
- Control electromagnet with housing
- Actuating rod/ plunger
- Magnetic force sensor/flux detector
- Control piston
I/H converter’s working is based on electromagnet which is energized by 24 Vdc and in turn creates a force on the actuating rod. When (4 to 20) mA signal is applied to I/H converter, its controller and amplifier adjust the magnetic force to a pressure directly proportional to the input signal. This force is measured by a semiconductor which serves as the unit’s magnetic force sensor/flux detector. Magnetic force lines penetrating this element produce a proportional output voltage (the “Hall effect”). The output voltage is looped back to the converter’s controller and compared to the set value, W. If the unit senses a difference between the input signal and the feedback signal, the controller and amplifier correct the magnetic force so that the difference is zero. The magnetic force adjusts the actuating rod to the appropriate position. As a result of this precise control technology, the I/H Converter’s output line always contains the exact pressure needed to position the valve. Here the desired output pressure range is set by means of two potentiometers.