Filename: Hydraulic Valve Interface Information.docx Date: 04/02/2014 Version: 2.0 Hydraulic Valve Interface Products Hydraulics provides a wonderful way of generating very large forces to move and control. Adding control using PLCs and other electronic devices is now common practice and many of the modern valves have control electronics built in. On the downside, hydraulic valves can be quite costly and so if we can add control to older, existing valves, many automation projects become be financially viable. Often the valves already have some form of drive or control but often not directly with 4-20 ma or other control level signals suitable for modern automation. A hydraulic valve normally has a fluid control spool which is moved by the magnetic flux produced by the one or more coils in the valve. Generally, a spring return moves the spool back to the rest position of zero of neutral flow. The spool directs the hydraulic oil flow in the forward and sometimes reverse directions. This is very similar to the operation of a DC motor with the spool analogous to the motor armature and the valve coil similar to the motor windings. Again, similar to a DC motor, sometimes only one direction of rotation is needed (mono-polar operation) and in others the valve must operate in both directions (bipolar). As with all motors, the torque (rotational force) is proportional to the current and in the case of hydraulic valves the spool position (and hence oil flow) is proportional to the current flowing through the coil windings. 1 Page
Sometimes voltage control is used for hydraulic valves, which is generally satisfactory, but the current will be affected by the coil temperature and variations in coil resistance from valve to valve and so current control is preferred. Since the valve coil is an inductor, pulses of current can be applied for control and the inductance averages out the current (integrates) to produce smooth control. So it is quite common to use Pulse Width Modulation (PWM) control with hydraulic valves. Benefits of PWM control are: Less heating of the control circuitry; Bipolar operation is an easy add-on and it is not too difficult to avoid valve sticky-ness (stiction). This is what happens when a slowly increasing current is applied and nothing happens for a while, the spool is stuck in place and then eventually there is enough force to overcome this stiction and the oil starts flowing. Dither is applied where when the valve is at the no-flow position, the spool is kept free by applying the same backward and forward current so that the spool just buzzes around the no-flow position. High coil currents are easier to manage electronically. Drawbacks of PWM control: The circuitry is generally more expensive and less reliable; For small valve currents (less than 250 ma) linear control is cost-effective in terms of size and circuit complexity. It is important to note that for bipolar operation the valve coil must not be connected to the chassis or a general earth, negative or a 0 V connection and often a lot of electrical noise is generated. 2 Page
Features to consider when selecting a Hydraulic Valve Interface: What is the valve current range required? Does the valve current need to be bi-polar? Is PWM control specifically required or desirable? Does it require the Danfoss type proportional/ratiometric or 25% to 75% voltage control input? What supply do you have available 12 VDC (10 to 13.8 VDC); 24 VDC (22 to 28 VDC); 110 or 230 VAC? Is galvanic isolation required between the valve and the controller? What input is best for the hydraulic valve interface 4-20 ma, ±10 V etc. Is ramping required to limit the rate at which the hydraulics is activated? Do you require dither? Is a DIN rail mounting device required is does the application need a robust, sealed unit for a high vibration environment? Are there any other special inputs or control functions required? What are the environmental conditions - operating temperature, vibration, dust, moisture, oil and dirt? One should always remember the valve coil inductance effects this can be spikes when switching on and off suddenly, magnetic fields which may be generated and noise generated by the switching valve current. Isolation can also be very important and often solve problems which cannot be explained or cured easily. Imbedded interface units, where the valve electronic interface and drive circuitry is integral to the valve, as is modern practice, has a few problems. It is tricky, if not impossible, to keep the electronics cool as the electronics, generally, will end up operating close to the oil temperature with a considerable reduction in reliability and life span. Also with imbedded electronics, it is generally impossible to repair. At elevated temperatures a silicon device can fail catastrophically, but even if it doesn't, its electrical characteristics frequently undergo intermittent or permanent changes. Most devices are not certified to function properly beyond 50 C-80 C (122 F-176 F). The life of an electronic device is directly related to its operating temperature. Each 10 C (18 F) temperature rise reduces component life by approximately 50%. Conversely, for each 10 C (18 F) temperature reduction the component life is increased by 100%. Therefore, it is recommended that all electronic components be kept as cool as possible for maximum reliability, longevity, and return on investment. 3 Page
Danntech products which could be useful are: Hydraulic Valve Signal Converters NB1, 2, 3 & 4-24/12 VDC These converters have been specifically designed to work with valves that require voltage proportional/ratiometric voltage control (25% to 75% - as per Danfoss type valves). The four input types are: 4-20 ma, +/-10 V, 0-10 V and 0-12V with 25% - 75% (voltage proportional) outputs. Hydraulic Valve Signal Converter 24/12 VDC Designed to provide process instrumentation interface for hydraulic valves. Converts 4-20 ma, 0-10 V, ±10 V and 0-12 V to 25% to 75% of the DC supply. 11 to 30 VDC operation. Suited for industrial control and automation systems. Compact, economical, DIN rail mounting. Neutral point adjustment. Price: R975 4 Page
Hydraulic Valve Interface Module 24/12 VDC Microprocessor based module designed to provide a variety of interface options between standard process control signals and most hydraulic valves. Inputs: Resistance - 0 to 100 Ω minimum to 0 to 10 kω maximum (joystick or potentiometer). Current - 0 to 20 ma, 4 to 20 ma or from 1 ma up to 500 ma DC. Voltage - 0 to 10 V, 25% to 75% or from 100 mv up to 100 VDC. Outputs: Current - from 0 to 500 ma (typically 4 to 20 ma, 0 to 85 ma, 0 to 480 ma). Voltage - 25% to 75 %, 0 to 10V. Interfacing to hydraulic valves is generally never simple. To make things a little easier, Danntech have designed a multi-purpose Hydraulic Valve Interface Module with a variety of inputs, various outputs with an adjustable ramping up and down functions with times up to 100 seconds. Example Mode 2 operation - Ramp Up/Down with External Control Various inputs can be used such as: resistance 0 to 100 Ω minimum to 0 to 10 kω maximum (joystick or potentiometer), currents from 0 to 20 ma, 4 to 20 ma or anything from 1 ma up to 500 ma DC, voltages from 0 to 10V, 25% to 75% or anything from 100 mv up to 100 VDC. (Specifically the Danfoss valves and joysticks can be used). Outputs can be current - anything from 0 to 500 ma typically: 4 to 20 ma, 0 to 85 ma, 0 to 480 ma or voltage - 0 to 10 V or 25% to 75%. The unit occupies only 25 mm of space on a DIN rail and can be either 12 V or 24 V DC powered. Being microprocessor based, the unit can be adapted for special functions if required. It can also be used for soft-start applications with internal setpoint control using an internal trimpot or external resistance control. The setpoint determines the maximum output value or the output control value. 5 Page
The Hydraulic Valve Interface Module can also be used as a signal converter with inputs of resistance, 4 to 20 ma, 0 to 10V or 25% to 75% and outputs either 4 to 20 ma, 0 to 10V or 25% to 75%. The converter will inherently include the ramping functions. On request from one of our clients some time back, we have included an Output Invert Option do that by changing the connection of one terminal the output signal is inverted. This is used when the way the valve is piped up produces the inverted action, so it s quick and easy to change without redoing the piping. Control Input can be either open circuit, switched to 0V or switched to Vcc. This controls the Ramp Up and Ramp Down to and from Setpoint. When Control Input is open the output will ramp to the setpoint value, when switched to 0V or left open the output ramps down to minimum output, when switched to +Vcc the output ramps to the setpoint value. Hydraulic Valve Interface Module 24/12 VDC Microprocessor based module designed to provide a variety of interface options between standard process control signals and most hydraulic valves. Inputs: Resistance - 0 to 100 Ω minimum to 0 to 10 kω maximum (joystick or potentiometer). Current - 0 to 20 ma, 4 to 20 ma or from 1 ma up to 500 ma DC. Voltage - 0 to 10 V, 25% to 75% or from 100 mv up to 100 VDC. Outputs: Current - from 0 to 500 ma (typically 4 to 20 ma, 0 to 85 ma, 0 to 480 ma). Voltage - 25% to 75 %, 0 to 10V Price: R2 750 Process Signal to Pulse Width Converter 24/12 VDC Converts process signals to Pulse Width output at the applied voltage. Choice of four frequencies, the pulse width is proportional to the input signal. Galvanically isolated and fuse protected. Designed to provide an isolated, compact, Pulse Width output to control hydraulic valves and electric motors using voltages from 10 to 30 VDC and current up to 5 A. 6 Page
Process Signal to Pulse Width Converter 24/12 VDC Converts process signals to Pulse Width output at the applied voltage. Fixed frequency at 200 Hz, the pulse width is proportional to the input signal. Galvanically isolated and fuse protected. Price: R2 750 High Current Output Signal Converter Provides either a voltage or current output of up to ±10 V at up to ± 350 ma or a higher current version up to ± 1.1A. Output can be either constant voltage or constant current. Linear control of output current and voltage, not switched mode. Interface to bipolar hydraulic valves. This specialized converter uses a powerful microcontroller to convert, process, isolated and generate an output which can be either for voltage or current control. The output is linear and can be anything between ±10 V and ±350 ma (or ±1.1 A). Can be used for Hydraulic Valves, driving small actuators, generating test currents, motor 7 Page
control, electrochemical cell control, etc. It can also be used to generate various waveforms up to about 200 Hz with RS232 and RS485 connection. High Current Output Signal Converter Provides either a voltage or current output of up to ± 10V at ±350 ma (or ±1.1 A). Output can be either constant voltage or constant current. Linear control of output current and voltage, not switched mode. Interface to bipolar hydraulic valves. Price: R3 975 DC Current Control Unit Compact, precision linear current control up to 20 V at 2 A DC. Output control with low noise, linear operation. External DC power supply. Various control signal options. Polarity reversal and output ON/OFF with digital input control. Current and voltage feedback outputs. Overtemperature protection with automatic shutdown. This product has been designed to provide the various current control and monitoring functions required for any system requiring bipolar current control between 0 and 2 A DC at up to about 20 V. Suited for use with Hydraulic Valves, Motors or the Electrochemical Cell Control. The DCCU provides a controlled current output from 0 to 2 A when powered from a 24 V 2.5 A DC power supply. It requires this external power supply to supply the load as well as the internal control circuitry. Inherently this means that the load, the output monitoring, the 0-5 V control input and the process signal inputs are connected to the 0 V terminal of Vin. Therefore there is no galvanic isolation between any of these connections. However the PWM input, the OUTPUT ON/OFF and the POLARITY REVERSE inputs are optically isolated and therefore when using this with the Pulse Width Modulated (PWM) input (such as from the Danntech Measurement and Control Interface, MCI [website link click here]) and a single 24 V 2.5 A power supply one can achieve isolation from the load, the power supply and the MCI. If the monitoring outputs are going to be used one should use an isolating signal converter [website link click here] to achieve isolation. 8 Page
Internally the series regulating element (a FET) is fan cooled, as it can dissipate up to 20 V at 2 A = 40W. If the fan should fail or the power dissipation be exceeded and the temperature rises above a preset level then the unit will switch off automatically until the temperature decreases when it will switch back on again. This temperature threshold is set to approximately 70 C. An output voltage monitoring circuit indicates when the output voltage goes above about 18 V typically when the load is disconnected or the output voltage compliance is exceeded (more than about 10 Ω). An LED indicates when this occurs. DC Current Control Unit Compact, precision current control up to 20 V at 2 A DC. Output control with low noise, linear operation. External DC power supply. Various control signal options. Polarity reversal and output ON/OFF with digital input control. Current and voltage feedback outputs. Overtemperature protection with automatic shutdown. Price: R4 250 Multi-Purpose Pulse Width Modulating (PWM) controller. Suitable for customized or specialized control of hydraulic valves, servomotors and electrochemical processes. Provides bipolar or monopolar PWM output, motor speed and direction control and process signal to current and/or power. Designed for applications such as servo-motor control, hydraulic valve control and other electrochemical processes and polar modulation type of functions health, water quality, etc. Has features such as bipolar output up to ±26 V up to 2 A, constant current or voltage control, four quadrant control - DC to 10 khz, pulse width control from 0 to 100% with resolution of 0.5%, output frequency control from 0 to 5 khz with resolution better than 20 Hz, 9 Page
independent output bridge voltage control from 6 to 26 V, digital temperature sensor for thermal protection located close to output power FETs, measurement and feedback of output voltage and output current, 10 segment bi-colour LED bargraph for display of any parameter, three display LEDs on top side with same surface mount LEDs to display LED status on component side, DC in 20 to 30 VDC or AC in 15 to 25 VAC, two analogue inputs with signal conditioning to accommodate current inputs from 0 to 100 ma and voltage inputs 0 to 100 VDC (standard inputs: 0-20 ma, 4-20 ma, 0-10 V), push button input, one digital input which can also be configured as a digital output, two digital inputs which can be used for pulse inputs (0-5 V, 0-12 V or 0-24 V), three 10 position rotary switches for parameter selection or programming, one relay output, real time clock for any timekeeping functions, 80 x 100 x 35 mm (width x length x height). Pulse Width Modulator Control Module Suitable for customized or specialized control of hydraulic valves, servomotors and electrochemical processes. Provides bipolar or monopolar PWM output, motor speed and direction control and process signal to current and/or power. Price: POA We here at danntech are ready to assist you our new potential customer or existing customer in any way possible. So please do not hesitate to contact us for assistance Marie or Mike on (011) 792-1239 or sales@danntech.com 10 Page