Box chopper amplifier BOE Description The box chopper amplifier is an always energised Pulse-Wide-Modulated (PWM) H-Bridge for to drive inductive loads with bipolar current in according to an analogue input. Adjustments for servo valves with different rated current and different input signals are available. With the high chopper frequency of 40 khz it is especially useful for dynamic servo valves. The dither signal, which is necessary for servo valves, is generated in the box and can be adjusted with Pots. The box is in an electronic housing and can be mounting on DIN rails. Technical data 1. Power supply: Nominal supply voltage: Permissible range Internal power loss Current consumption: 24 V DC 18V... 28 V 2 W 50mA plus coil current 2. Output current Order code 2 (see order code on page 2) -300 ma... 0 ma...+300 ma, adjustable with Pot from ±200mA to ±1000 ma 3. Input signals Type (U/I) range Input resistance order code voltage -10V... 0... +10 Volt Ri 1 Mohm 0 current +0... 10... +20mA Ri 50 ohm 1 current +4... 12... +20mA Ri 50 ohm 2 current -10... 0... +10mA Ri 50 ohm 3 current -20... 0... +20mA Ri 50 ohm 6 current -100... 0... +100mA Ri 5 ohm 8 4. Technical details Chopper amplifier for inductive loads with current controller and adjustable dither generator for servo valves. Potentiometer on the front side for all related adjustments 5. Dimensions Breadth: 27 mm recommended lateral row-spacing 40 mm Length: 79 mm high above rail: 85,5 mm Mass about 100g 6. Environment IP 40, for mounting in an electrical cabinet or junction box temperature range: 20C to +60 C 7. Connection Pin 1 Signal input (connect to GND) Pin 2 Signal input + Pin 3 power GND Mass Pin 4 Servo conn. Pin 5 Servo conn. + Pin 6 power supply +24V Remark: Connect signal input (Pin 1) and supply GND (Pin 3) with low impedance connection. Specification subject to change without notice! All rights reserved page 1 of 5
8. bloc diagram 9. Order code BOE XXX 025 x 5-1A order no. xxx Legend: 1 2 3 4 5 6 1 = Type 2 = rated current, possible models xxx = stock type, adjusted on ±300 ma 200 = 200 ma 300 = 300 ma 650 = 650 ma 999 = 999 ma 3 = housing code 025 = UEGM housing type 27 mm breadth 4 = code for input signal, possible models 0 = 0... ±10 Volt 1 = 0... 20mA 2 = 4... 20mA 3 = 0... ±10mA 6 = 0... ±20mA 8 = 0... ±100mA (Moog, Dowty valve input) 5 = code for power supply 5 = unipolar power 24V 6 = code for construction level 1A Specification subject to change without notice! All rights reserved page 2 of 5
10. Example of order code Type order no. remarks BOE xxx-025-0-5-1a 36738 stock type, voltage input, adjusted to 300mA BOE 650-025-0-5-1A 12729 voltage input, adjusted to 650mA BOE 999-025-0-5-1A 1060101 voltage input, adjusted to 1000mA BOE 999-025-1-5-1A 1060101 single side current input, current out adjusted to 500...1000mA BOE 050-025-2-5-1A 11662 current input 4-20mA, adjusted to 50mA BOE 300-025-2-5-1A 10698 current input 4-20mA, adjusted to 300mA BOE 050-025-6-5-1A 1007990 current input 0-±20mA, adjusted to 50mA BOE xxx-025-6-5-1a 1006558 current input 0-±20mA, adjusted to 300mA BOE 999-025-6-5-1A 12325 current input 0-±20mA, adjusted to 1000mA 11. Front view and picture 12. Technical hints Connection cable Cable for input signal and for servo valve current could be a shielded cable and the end of the cable should be grounded Test point: Test points are 2 mm jacks on front side. Measured value 5V is a current of 1000mA with a max tolerance of 10% Valve direction: The servo valve direction can be changed by changing the wire on pin 4 and pin 5 Specification subject to change without notice! All rights reserved page 3 of 5
13. Adjustment hints Rated current adjustment The BOE amplifier is delivered with the specification according to the name plate data If you need a recalibration of rated current, you have these measuring possibilities: a) Direct current measuring Use an A-meter in the line to the coil. This is the most accurate adjusting. b) Measuring Shunt connect in the line to the coil for example with a 1 Ohm resistance. Evaluate the voltage loss with a V-meter or an oscilloscope. c) Test point Use the test point voltage as information for the current. This voltage can have a measuring error of about 10%. Proceed: Connect 100% input signal to BOE and adjust the rated current (max current) with pot P3. Verify the zero point ( 0%) and max point again and correct the output coil current with pot P1 or pot P3. If you don t have an original valve coil, use instead an electric relay. A current adjustment in short circuit without any load is not recommended. If you adjust an over current under this test conditions, you have the rink to burn the internal inductors and current sense resistance. Dither adjustment The need of Dither a) Reduce of valve hysteresis From the mechanics it is well known, that if a motion starting from zero have a higher friction compare to a still in motion movement. Also the internal servo piston has a lower friction and hysteresis if he is still in motion. Therefore all electronic equipment has a dither adjustment for Servo- and Proportional valves. An optimal Dither adjustment increases the closed loop precision and the reliability of the hydraulic system. b) Reduce of pollution sensivity With a little movement of the piston all small pollution particles in the oil can bypass on the closed ports of the valve. This is very important for all static applications. In dynamic application mostly you do not need a dither. Specification subject to change without notice! All rights reserved page 4 of 5
Dither frequency The Dither frequency is a f actory setting to about 200 Hz. This is a frequency with the internal piston can move, but bigger mass objects like cylinders cannot follow. Normally the frequency is not so important. Only if you have for example an interference with mains supply frequency, you can change the frequency with Pot P4. The frequency range is from 40Hz up to 500Hz. Dither amplitude The dither is generated as an AC voltage and is added to your signal input. Factory setting for amplitude is close to zero. The adjustment range is from 0 to 10% of rated current range with the 15-turn Pot P2. On the test point on front side you can measure the dither. (Recommend range see at the light green cells in the below table) Turns 1 2 3 4 5 6 7 8 9 10 11 12 13 14 turns AC eff 5 10 20 40 60 80 95 107 110 115 120 125 130 135 [mv] Per cent 0,3 0,7 1,3 2,7 4,0 5,3 6,3 7,1 7,3 7,7 8,0 8,3 8,7 9,0 in % Dither measurements Without the need of an oscilloscope you can measure the dither with a multimeter in AC voltage range. Practical adjustment The effect of the dither is related to the oil pressure and the among of oil in the cylinder. It is also related to the servo valve flow capacity in relation to the cylinder size. Sometimes there is a mechanical resonance between length of pipe and the dither. All these facts have a relation to the dither adjustment. So it is heavy to give a general rule for the correct dither amplitude. Most of servo valve suppliers recommend a value of about 2% to 5 % of rated current. We recommended adjusting about 5 turns stated from zero. Then you can feel (or hear) a little bit the dither on the valve housing or on the pipes close to. This is sufficient in most cases. Use of the dither for valve cleaning If you think the control is bad do to a too big hysteresis caused of pollution, you can use the dither for cleaning the valve. Turn the Dither amplitude to max adjustment (full 15 turns counter- clockwise) and wait for about 5 minutes. Then adjust back to the standard amplitude. If then the control and resolution is better, you have the evidence that you have a pollution problem with the oil. To overcome this on a long term basis you have to check the oil quality and exchange or clean the oil. The other alternative is to use a higher dither as a standard. Disadvantage of dither A too big dither amplitude can vibrate the hydraulic pipes and cause to a broken pipe. Caution: Fix all pipes carefully with clamps. The dither can increase the abrasion on the internal spool. But the spool and sleeve system is supported by hydrostatic (oil) bearings. If oil quality is sufficient, a negative abrasion and a higher zero flow takes place only after years of operation. Specification subject to change without notice! All rights reserved page 5 of 5