Rexroth Bosch Group VT2000 Proportional Amplifier

VT2000 Proportional Amplifier Complete Guide: From Functional Principles to On site Troubleshooting

In industrial hydraulic systems, the control accuracy of proportional pressure valves directly depends on the performance of their electronic amplifiers. Bosch Rexroth's VT2000 series amplifiers are designed specifically for controlling direct acting and pilot operated proportional pressure control valves (without electrical position feedback). With the continuous operation of old equipment, many factories are still using VT2000 5X series or earlier 4X series amplifiers. When the amplifier malfunctions or needs to be replaced, engineers often face difficulties such as spare parts shutdown and missing documents. This article is based on the technical manual of VT2000, comprehensively analyzing its functional block diagram, terminal definitions, technical parameters, jumper settings, and on-site troubleshooting steps, helping hydraulic maintenance and system integration personnel quickly grasp the key points of using and replacing the amplifier.

Product positioning and core features of VT2000

VT2000 is a single channel proportional amplifier that adopts the European standard Euro card (100 × 160mm) size and is connected to the system through a 32 pin DIN 41612 male connector. The main design objective is to provide an adjustable current drive signal with ramp function for proportional pressure control valves. This amplifier is suitable for proportional pressure valves without electrical position feedback (i.e. open-loop control), which can change the spool position or pilot pressure by adjusting the electromagnetic current.

The core features include:

Differential input: can accept 0~+10V signals from PLC or other controllers, isolated from internal reference potential.

Additional command value input: 0~+9V (based on measuring zero position MO as a reference).

Slope generator: The time for ascending and descending slopes can be adjusted separately, and rapid slope can be forced through external contacts.

Clock type current output stage: outputs PWM modulated current with adjustable flutter frequency (100Hz or 200Hz) to reduce valve core friction.

Protection functions: reverse polarity protection of power supply, short circuit protection of electromagnetic cable, over temperature shutdown (no separate alarm signal).

Measurement socket: The front panel provides "w" (instruction value) and "I" (actual current value) test points for easy debugging.

This amplifier needs to be used in conjunction with an external power supply and card slot. Rexroth recommends using the VT3002-2X/32 single card slot (excluding power supply) and the VT-NE30-1X compact power supply (115/230VAC to 24VDC, 70VA).

Order code and version compatibility

The ordering code for VT2000 follows Rexroth's coding system. Although the complete code table is not listed in the document, important information is pointed out that the 5X series amplifier can be interchangeable with the 4X series under factory settings, provided that the ramp time is set to 5 seconds and the clock frequency is set to 200Hz. If you want to replace the 4X with 5X, you need to order an additional blind plate with a width of 4TE (due to differences in front panel width). Users should pay attention to checking the settings of the original system to ensure that the new amplifier jumper configuration is consistent with the old machine.

Detailed explanation of functional block diagram and signal flow

In order to effectively troubleshoot, it is necessary to understand the signal processing link inside VT2000. Below, we will explain one by one according to the signal flow direction.

3.1 Instruction value input level

The amplifier provides two input channels for instruction values:

Command value input 1: Voltage range 0~+9V, reference potential is MO (measure zero position). This input can be obtained by dividing it with an external potentiometer using an internal+9V regulated power supply. If the user uses an external potentiometer, the "Gw" potentiometer on the front panel of the amplifier must be adjusted to the maximum or to the position corresponding to the required maximum pressure.

Instruction value input 2 (differential input): voltage range 0~+10V, input resistance 100k Ω. Differential input is suitable for external electronic devices (such as PLC) and amplifiers that are not grounded together. When using differential input, two signal lines (28c and 30ac) must be connected or disconnected simultaneously.

The two command values are summed internally ([2]) and then sent to the command value attenuator (potentiometer "Gw" [3]) to limit the maximum output current (i.e. maximum pressure). The attenuated signal enters the ramp generator [4].

3.2 Slope Generator

The ramp generator converts step command values into ramp signals. The ramp time (from 0% to 100% command value) can be adjusted by two potentiometers to adjust the rise time and fall time respectively. The slope time range depends on the setting of jumper S1:

S1 jumper at "1s" position: ramp time 30ms~1s

S1 jumper at "5s" position: ramp time 30ms~5s

If the step amplitude of the instruction value is less than 100% (such as when the attenuator has been limited or the input is only 5V), the actual ramp time will be proportionally shortened. In addition, the up or down ramp can be forcibly shortened to the minimum value (about 30ms) through the external contact "ramp up/down" for emergency rapid response.

The output signal of the ramp generator is the internal current command value, which can be monitored at the measuring socket "w". The 100% instruction value corresponds to a+6V voltage (note that it is not 10V, which is easy to misunderstand).

3.3 Bias current superposition and current regulator

After the ramp signal is sent to the current regulator [5], it will be added to the bias current ("Zw" potentiometer R130). The bias current can be adjusted within the range of 0~300mA, used to overcome the dead zone of the valve or set the minimum pressure. Adjusting R130 can change the zero offset.

3.4 Clock output stage and jitter

The output of the current regulator is modulated by PWM (clock frequency of 100Hz or 200Hz, selected by jumper S2) and then sent to the output terminal of the electromagnet. This clock like current generates a superimposed flutter signal (dither) in the electromagnet, which helps to reduce the static friction and hysteresis of the valve core. The maximum current of the output stage is 800mA (+10%/-5%), and the corresponding load resistance is 19.5 Ω (the cold resistance of the electromagnet is about 20-30 Ω). The output stage has short-circuit protection and will automatically shut down when overheated - but will not emit a fault signal, which needs to be noted when troubleshooting "sudden valve failure".

The actual electromagnetic current can be monitored at the measuring socket "I", with 800mA corresponding to 800mV (i.e. 1mA/mV). This is a very intuitive proportional relationship.

3.5 Internal power supply

The amplifier is powered by 24VDC (allowing+40%/-5%, i.e. 22-35V). Internally generated ± 9V regulated power supply, with+9V used for external potentiometer power supply and -9V used as a reference for measuring zero position MO. Attention: MO has been raised by+9V relative to the 0V power supply and is not isolated. Therefore, it is absolutely forbidden to connect MO to a 0V power supply, otherwise it will short-circuit the internal power supply. Only high internal resistance instruments (Ri>100k Ω) can be used for measurement.

Terminal allocation and wiring guide

VT2000 adopts a 32 pin male connector (DIN 41612, D-type). Although the document does not provide a complete list of terminals, key terminals can be inferred from the troubleshooting steps and diagrams:

Terminal signal description

24ac+24V power supply working voltage positive pole

18ac 0V power supply working voltage negative pole

10ac+9V output for external potentiometer use

12ac instruction value 1 input 0~+9V (relative to MO)

28c differential input+0~+10V

30ac differential input - reference potential

22ac electromagnet+connected to one end of the proportional valve coil

20ac electromagnet - other end of the wiring coil

6,8 Ground/Shielded Connection to System Grounding

16ac, 14mc slope external contacts are used for fast slopes (please refer to the complete manual for details)

Key points of wiring:

Electromagnetic connection wires must not use plugs with freewheeling diodes or LED indicator lights, otherwise it will interfere with PWM output or generate reverse voltage and damage the amplifier.

The instruction value cable must be shielded, with the shielding layer grounded on the amplifier side and the other end suspended.

Electromagnetic cables should also be shielded (recommended). When the length is ≤ 50m, use LiYCY 1.5mm ² cable. If it is longer, consult the manufacturer.

Keep a distance from strong electrical cables (power lines) and at least 1 meter away from antennas, radio stations, and radar equipment.

Jumper setting and potentiometer function

There are multiple jumpers on the VT2000 board (located on the PCB and labeled with nameplates) used to configure the basic working mode. Users should record the actual settings and keep them the same when replacing.

5.1 S1- Selection of Slope Time Range

Position "1s": The maximum slope time is about 1 second

Position "5s": Maximum ramp time of approximately 5 seconds

The factory setting is usually 5 seconds to ensure compatibility with the 4X series.

5.2 S2- Clock Frequency Selection

100Hz

200Hz

The factory is set to 200Hz. Different valves may have requirements for vibration frequency, and too high or too low can cause valve core vibration or increased hysteresis.

5.3 Other jumpers (such as instruction value source selection)

The document mentions that if using an internal command value potentiometer (i.e. an external potentiometer connected between 10ac and 12ac), a jumper must be inserted between 10ac and 12ac. This jumper is used to lead the internal+9V to the command value input. The specific location needs to refer to the markings on the PCB (the circles in the figure represent user settings, and the solid circles represent factory settings).

5.4 Adjustable components on the front panel

Gw potentiometer: maximum command value attenuation (i.e. maximum current/pressure limit). Increase clockwise.

R130 (Zw): bias current regulation, located on the PCB (not the front panel). Used to set the zero point (minimum pressure). The adjustment range is 0~300mA.

5.5 Measuring sockets

w: Internal command value voltage, 0~+6V corresponds to 0~100%.

I: The actual electromagnetic current corresponds to 800mA at 800mV.

Summary of Technical Parameters (Engineering Key Values)

Parameter values

Working voltage 24 VDC (allows 22-35V, including+40%/-5%)

Power consumption<25 VA

Current consumption<1 A

Fuse 2.5 A slow melting (T-shaped)

Command value input 1 0~+9V (refer to MO)

Command value input 2 (differential) 0~+10V, Ri=100k Ω

Slope time adjustable range 30ms~1s or 5s

Maximum electromagnetic current 800mA (+10%/-5%)

Electromagnetic coil resistance 19.5 Ω (rated), actual cold state about 20-30 Ω

Bias current range 0~300mA

Clock frequency 100Hz or 200Hz (± 10%)

Internal voltage regulation output ± 9V ± 1%, ± 25mA

Measure socket w 0~+6V (100% command value)

Measure socket I 800mV corresponding to 800mA

Connector 32 pin DIN 41612, D-type

Card size Euro card 100 × 160mm

Front panel height 3 HE (128.4mm)

Front panel width component side: 3TE; welding side: 1TE

Working temperature 0~50 ° C

Storage temperature -25~+85 ° C

Weight approximately 0.1kg

On site troubleshooting steps

When the proportional pressure valve does not work or responds abnormally, the VT2000 amplifier should be checked in logical order. The following steps refer to the 8 checks in the manual and are expanded based on practical experience.

Step 1: Check the working voltage

The voltage between terminals 24ac and 18ac should be between 22-35V DC. If there is no voltage, check the external power supply, card slot connection, and fuse.

Step 2: Check the amplifier fuse

The VT2000 onboard fuse is a 2.5A slow melting fuse. Remove the card and measure the continuity with a multimeter. If the circuit is blown, the cause needs to be investigated: short circuit of the electromagnet, cable damage, or output stage failure. Attention: After replacing the fuse, the same specification (2.5A T-type) must be used, and fast melting cannot be used as a substitute.

Step 3: Check the internal ± 9V voltage

Measure whether there is ± 9V at the measuring socket or corresponding testing point. If not, it may be a fault in the power circuit on the board (such as damaged voltage regulator or capacitor). This step requires the use of test points on the PCB, which can typically measure+9V output (terminal 10ac for MO).

Step 4: Check command value input

If using an external potentiometer: check if there are jumper wires between 10ac~12ac? Is the wiring of the potentiometer correct (10ac and MO at both ends, 12ac on the sliding arm)? Is the Gw potentiometer set to zero?

If differential input is used: check if the voltage on 28c and 30ac is 0~+10V? Are both wires connected or disconnected at the same time? Is the reference potential correct?

Step 5: Check the electromagnet circuit

Unplug the amplifier (power off) and measure the resistance between terminals 22ac and 20ac. Normally, it should be 20~30 Ω (temperature of the line of sight coil). If it is infinite (open circuit) or close to 0 Ω (short circuit), the valve coil or cable is faulty. If the resistance is normal, check if the cable is short circuited to ground.

Step 6: Monitor and measure the socket

Given an instruction value (e.g. 5V), the voltage of the "w" socket should rise with the ramp up to the corresponding value (e.g. 5V input corresponds to about 3V? Note the conversion relationship between input and w: 100% instruction value corresponds to 6V, and 100% instruction value may be obtained by attenuating and ramping the 9V or 10V input. During actual debugging, given the maximum command value, adjust Gw to reach 6V, and the output current should be 800mA.

Measure the voltage of the "I" socket, which should be equal to one thousandth of the actual output current (mA) value. For example, when outputting 400mA, the I socket should be 400mV.

Step 7: Check the over temperature shutdown

If the output stage temperature is too high (such as working at full current for a long time and poor ventilation), the internal thermal protection will turn off the output, but the "I" socket may still display a command value? In fact, the thermal protection cuts off the output stage, and the current detection may return to zero. At this point, it will automatically recover after cooling. There is no separate alarm, so it is easy to be ignored.

Step 8: Check the external contacts of the slope

If the external quick ramp function is used, check if the contact accidentally closes, causing the ramp time to be forcibly shortened and causing the valve to respond too quickly.

Replacement and engineering precautions

8.1 Replacement of discontinued models

The VT2000 4X series has been discontinued, with 5X serving as a replacement. Attention should be paid when replacing:

Ensure that the jumper settings (ramp time range, clock frequency) are the same as the old card.

If the width of the front panel is different (4X is different width), blind plates need to be ordered.

Check if the power supply is still 24VDC (the old system may have used other voltages).

The original 4X may not have over temperature protection, while the 5X does, but it will not affect its functionality.

8.2 Installation precautions

The amplifier must be plugged in and out in a power-off state.

Do not use a plug with a freewheeling diode to connect the electromagnet, as it may damage the PWM waveform and potentially damage the output stage.

When measuring, only high internal resistance instruments (≥ 100k Ω) can be used, and ordinary pointer multimeters may cause measurement errors.

Measurement zero position MO cannot be connected to a 0V power supply! This means that the oscilloscope ground clip cannot be randomly connected to the MO, and differential probes or isolation channels should be used instead.

8.3 Electromagnetic Compatibility (EMC) and Wiring

Command value cable shielding layer single ended grounding (amplifier side).

The amplifier itself is grounded through terminal 6 or 8. If there is no system ground, ground the 0V power supply.

Electromagnetic cables should also be shielded and laid separately from power cables.

Maintain a distance of at least 1 meter from radio, radar, and other equipment.

8.4 Safety related

The electrical signals (such as actual values) derived from control electronic devices shall not be used to switch safety related machine functions. Pressure safety still relies on independent mechanical safety valves or designs that comply with prEN 982 standards.

Common Failure Modes and Solutions

9.1 The valve does not move at all, and the measurement of the "I" socket is 0

Check for 24V power supply; Is the fuse blown.

Check if the instruction value is actually sent (use a multimeter to measure 12ac or 28c for MO).

Check if the Gw potentiometer has been mistakenly adjusted to the minimum.

Check if the amplifier is overheated (cool down and try again).

9.2 The valve can operate but the pressure is low, and even the maximum command value cannot reach the system pressure

Measure whether the "w" socket reaches 6V at the maximum command value. If not, adjust the Gw potentiometer clockwise to increase.

Measure whether the "I" socket reaches 800mV. If it is below 800mV but "w" is already 6V, it may be due to output stage current limiting or high electromagnetic resistance (>30 Ω). Check the coils and cables.

Check if the bias current is set too high (Zw R130), causing the available adjustment range to be compressed.

9.3 Slow pressure response and long slope time

Check if the S1 jumper is in the "5s" position and if the ramp potentiometer is set too large. Try to reduce the slope time.

If the external rapid ramp contact remains closed, it will force a minimum ramp time (about 30ms) and the response will be fast. On the contrary, if the contact is disconnected, follow the set ramp time.

9.4 Pressure fluctuations or oscillations

Check if the clock frequency setting (100Hz or 200Hz) matches the valve. Some valves are sensitive to vibration frequency.

Check whether the shielding and grounding are good, and whether there is electromagnetic interference.

Check if the electromagnetic cable is too long (recommended cable not used for>50m).

9.5 After replacement, the amplifier cannot be inserted into the original card slot

Confirm if the card slot is VT3002-2X/32 type (standard Euro card slot). If it is a dedicated card slot, an adapter may be required.

How to obtain spare parts and technical support

Due to the fact that VT2000 belongs to an older series, Bosch Rexroth may have classified it as an outdated product. Users can obtain support through the following channels:

Contact Rexroth's official spare parts department to inquire if there are any remaining inventory or refurbished parts.

Use an independent repair service provider (such as Artisan Technology Group in the document source) to provide used or repaired equipment.

Consider upgrading to a newer amplifier series (such as VT-VSPA2 or VT-VRPA), but require reconfiguration of wiring and parameters.

When ordering second-hand or refurbished parts, be sure to confirm:

Complete model (VT2000 5X)

Whether the jumper settings comply with the application (the supplier may be required to pre configure according to the settings provided by the user)

Is there a test report attached (especially for output current accuracy and ramp time)