Electrohydraulic valve designs employ a number of different electrical connections. Mechanical Feedback Valves utilize the simplest electrical connections, while Electrical Feedback Valves can be more complex with different command signals, supply voltages and techniques to monitor actual spool position being employed. Most valves can be segmented into the following categories:
Rated Current and Coil Resistance: The specified input of either polarity to produce rated flow, expressed in milliamperes (mA). Rated current is specified for a particular coil configuration (differential, series, individual or parallel coils) and does not include null basis current.
Mechanical Feedback Standard Electrical Configuration: Standard electrical connections and electrical polarity for flow out of left control port when viewing valve from pressure side area are:
single coil: A+, B-; or C+, D
series coil: tie B to C; A+, D
parallel coils: tie A to C and B to D;
[A & C]+, [B & D]-
Coil Connections: A four pin electrical connector that mates with a MS3106R14S-2S or equivalent is standard. All four coil leads are available at the connector, allowing external connections for signal, series, or parallel coil operation.
Coil Connections : A four pin electrical connector that mates with a MS3106R14S-2S or equivalent is standard. All four coil leads are available at the connector, allowing external connections for signal, series, or parallel coil operation.
Servoamplifier : A Servovalve responds to input current. Therefore, in order to reduce the effects of coil resistance variations, a Servoamplifier with high internal impedance (as obtained with current feedback) should be used.
Dither: A small amplitude, high frequency sinusoidal signal may be used to reduce friction and hysteresis effects within the valve, improving system performance. If used, the peak-to-peak amplitude should be less than 10% of rated signal. Since the desired frequency is dependent on the valve style, consult factory for recommended frequency.
Coil Impedance : The two coils in each Servovalve are wound for equal turns with a normal production tolerance on coil resistance of ±12%. Copper magnet wire is used, resulting in a coil resistance that will vary significantly with temperature.The effects of coil resistance changes can be essentially eliminated through the use of a current feedback Servoamplifier having high output impedance. Inductance is determined under pressurized operating conditions and varies greatly with signal frequencies above 100 Hz.
Intrinsically Safe : Optional intrinsically safe designs are available for most standard valve models.These designs have been granted both entity and loop approval by Factory Mutual(FM) and Cenelec.