Bosch Rexroth VT-MRMA1-1 User manual

Operating instructions
RE 30214-B/03.2019
Replaces: 03.2017
English
VT-MRMA1-1
Analog amplifier module

The data specified only serve to describe the
product. No statements concerning a certain
condition or suitability for a certain application
can be derived from our information. The
information given does not release the user
from the obligation of own assessments and
verification. It must be remembered that our
products are subject to a natural process of
wear and aging.
© This document, as well as the data,
specifications and other information set forth in
it, are the exclusive property of Bosch Rexroth.
It may not be reproduced or given to third
parties without its consent.
An example configuration is shown on the title
page. The delivered product may, therefore,
differ from the product which is pictured.
The original operating instructions were
created in the German language.

RE 30214-B/03.2019, VT-MRMA1-1, Bosch Rexroth AG
3/52Content
Content
1 About this documentation 5
1.1 Validity of the documentation 5
1.2 Required and supplementary documentation 5
1.3 Representation of information 5
1.3.1 Safety instructions 5
1.3.2 Symbols 6
1.3.3 Terms used 6
1.3.4 Abbreviations used 6
2 Safety instructions 7
2.1 About this chapter 7
2.2 Intended use 7
2.3 Improper use 7
2.4 Personnel qualifications 7
2.5 General safety instructions 8
2.6 Product-specific safety instructions 8
3 General notes on damage to material and the product 10
4 Scope of delivery 11
5 About this product 12
5.1 Performance description 12
5.1.1 Block circuit diagram of the controller structure of the analog amplifier
module: 13
5.2 Product description 13
5.2.1 Components that can be connected 13
5.2.2 Function 14
5.2.3 Functions within the amplifier module 15
5.2.4 Controller and functions closely related to the controller 16
5.2.5 Actual value preparation 17
5.2.6 Monitoring functions 19
5.2.7 Measuring point changeover switch (15) 22
5.3 Identification of the product 22
6 Transport and storage 23
6.1 Storing the VT-MRMA1 23
7 Installation 24
7.1 Installation conditions 25
7.2 Required tools 25
7.3 Recommended accessories 26
7.4 Installing the VT-MRMA1 26
7.5 System-specific circuitry of the amplifier module 27
7.6 Overview of connections 27
7.6.1 Terminal assignment 28
7.6.2 Connection of the power supply unit 29
7.6.3 Connection of the pressure reducing valve 29
7.6.4 Connection of actual pressure value cables (pressure transducer) 30
7.6.5 Connection of the control 31
7.6.6 Plug-in screw connectors 31
8 Commissioning 33

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8.1 Adjustment, measuring and indicator elements 33
8.1.1 DIL switches 33
8.1.2 Potentiometers 37
8.1.3 Measuring signal and measuring point selector switch 38
8.1.4 LEDs 38
8.2 Commissioning instructions 39
8.3 Fine tuning of the complete system 40
8.4 Application example 41
9 Operation 43
10 Maintenance and repair 43
10.1 Cleaning and care 43
10.2 Maintenance 43
10.3 Repair 43
11 Demounting and replacement 44
11.1 Preparing demounting 44
11.2 Demounting 44
11.3 Preparing the components for storage or further use 44
12 Disposal 44
12.1 Environmental protection 44
13 Extension and conversion 44
14 Troubleshooting 45
14.1 How to proceed for troubleshooting 45
14.2 Erroneous states und error diagnostics 45
15 Technical data 46
16 Annex 47
16.1 Addresses 47
17 Alphabetical index 48

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1 About this documentation
1.1 Validity of the documentation
This documentation is valid for the following analog amplifier module:
• VT-MRMA1-1-1X/V0/0
This documentation is intended for fitters, operators, service technicians and plant
operators.
This documentation contains important information on the safe and appropriate
installation, transport, commissioning, maintenance, operation, removal and simple
troubleshooting of the product.
▶ Read this documentation thoroughly, especially chapter 2 “Safety instructions“
and chapter 3 “General notes on damage to material and the product“, before
working with the analog amplifier module.
1.2 Required and supplementary documentation
▶ Only commission the product, when you have the documents marked with the
book symbol at hand and have understood and observed them.
Table 1: Required and supplementary documentation
1.3 Representation of information
In order that this documentation allows you to work directly and safely with your
product, standardized safety notes, symbols, terms and abbreviations are used. For a
better understanding, these are explained in the following sections.
1.3.1 Safety instructions
This documentation contains safety notes in Chapter 2.6 “Product-specific safety
instructions“ and Chapter 3 “General notes on damage to material and the product“
as well as before a sequence of activities or instructions for action, which involve the
risk of personal injury or damage to equipment. The measures described for averting
the hazard have to be observed.
Safety notes are structured as follows:
SIGNAL WORD
Type and source of hazard!
Consequences in the case of non-observance
▶ Measures to avert the hazard
▶ <Enumeration>
Title Document number Type of
document
Analog amplifier module VT-MRMA1-1 30214 Data sheet
Pressure transducer for hydraulic applications, type HM20-2X 30272 Data sheet
Proportional pressure reducing valve with DC motor actuation 29173 Data sheet
Power supply unit type VT-NE30-2X 29929 Data sheet

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Bosch Rexroth AG, VT-MRMA1-1, RE 30214-B/03.2019
•Warning symbol: draws attention to a hazard
•Signal word: identifies the degree of hazard
•Type and source of hazard: identifies the type or source of the hazard
•Consequences: describes the consequences in the case of non-observance
•Precautions states, how the hazard can be avoided
Table 2: Hazard classes according to ANSI Z535.6-2011
Warning sign, signal word Meaning
DANGER Indicates a hazardous situation which, if not avoided, will
certainly result in death or serious injury.
WARNING Indicates a hazardous situation which, if not avoided, could
result in death or serious injury.
CAUTION Indicates a hazardous situation which, if not avoided, could
result in minor or moderate injury.
NOTICE Damage to property: The product or the environment can be
damaged.
1.3.2 Symbols
The following symbols refer to notes, which are not relevant to safety, but increase
the legibility of the documentation.
Table 3: Meaning of symbols
Symbol Meaning
If this information is disregarded, the product cannot be used or operated
in an optimum manner.
▶ Individual, independent action
1.
2.
3.
Numbered instructions for action:
The numbers indicate that the activities are to be carried out consecutively.
1.3.3 Terms used
The following terms are used in this documentation:
Table 4: Terms used
Term Meaning
VT-MRMA1 Analog amplifier module
UB Operating voltage
HM20 Pressure transducer
1.3.4 Abbreviations used
The following abbreviations are used in this documentation:
Table 5: Abbreviations used
Abbreviation Meaning
EMC ElectroMagnetic Compatibility
PE Protective Earth
PELV Protective Extra Low Voltage

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2 Safety instructions
2.1 About this chapter
The analog amplifier module has been manufactured according to good engineering
practice. There is, however, still a risk of personal injury or damage to equipment
if you do not observe this chapter and the safety instructions contained in this
documentation.
▶ Read these instructions completely and thoroughly before working with the
product.
▶ Keep this documentation in a location where it is accessible to all users at all
times.
▶ Always pass the product together with the required documentation to third
parties.
2.2 Intended use
The analog amplifier module is an electrical component.
You may use the product as follows:
• For controlling a DC motor-actuated proportional pressure reducing valve with
electrical position feedback, type (Z)DRS, size 6, component series 1X
The product is intended exclusively for professional use and not for private usage.
Operation according to the intended use also implies that you have read
and understood this documentation completely, especially chapter 2 “Safety
instructions“.
2.3 Improper use
Any use other than described in the section “Intended use” is considered as
improper and is therefore not permitted.
For damage resulting from improper use, Bosch Rexroth AG will not bear liability.
The risks arising from improper use lie exclusively with the user.
Improper use includes, but is not limited to the following, foreseeable misuse:
• operating the analog amplifier module outside the specified performance limits and
operating conditions, especially the prescribed ambient conditions;
2.4 Personnel qualifications
The activities described in this documentation require basic knowledge of electrics
and hydraulics as well as knowledge of the associated technical terms. To ensure
safe usage, these activities may therefore only be carried out by qualified personnel
or under the direction and supervision of qualified personnel.
Qualified personnel are those who can recognize possible hazards and institute
the appropriate safety measures due to their professional training, knowledge and
experience, as well as their understanding of the relevant conditions pertaining to
the work to be done. Qualified personnel have to observe relevant specialist rules
and have the required expertise.
With regard to hydraulic products, specialist knowledge means, for example:
• The ability to read and entirely understand hydraulic circuit diagrams,

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Bosch Rexroth AG, VT-MRMA1-1, RE 30214-B/03.2019
• the complete understanding in particular of interrelationships with regard to safety
equipment and
• knowledge of the function and structure of hydraulic components.
Bosch Rexroth offers qualifying training courses in specific fields. You can find an
overview of training contents on the Internet at:
http://www.boschrexroth.com
2.5 General safety instructions
• Observe valid regulations for accident prevention and environmental protection.
• Observe the safety regulations and rules of the country where the product is used/
operated.
• Use Rexroth products only in technically perfect condition.
• Observe all notes given on the product.
• Persons who install, commission, operate, demount or maintain Rexroth products
must not consume any alcohol, drugs or pharmaceuticals that may affect their
ability to respond.
• Only use accessory and spare parts approved by the manufacturer in order to rule
out personnel hazards arising from unsuitable spare parts.
• Adhere to the technical data and ambient conditions specified in the product
documentation.
• If unsuitable products are installed or used in safety-relevant applications,
unintended operational states may occur in the application that can cause personal
injury and/or damage to property. Therefore, use the product only in safety-relevant
applications such as in explosion protection areas or in safety-related parts of a
control (functional safety), if this use is expressly specified and permitted in the
documentation.
• You may commission the product only when it has been established that the final
product (for example, a machine or system), in which the Rexroth products is
installed, complies with national regulations, safety regulations and standards
relevant for the application.
• Observe safety-relevant information and information on risks in the operating
instructions of the manufacturer of the connected hydraulic system before
commissioning the analog amplifier module with a hydraulic system.
• Technical data, the connection and installation conditions can be found in the
product documentation and have to be strictly observed.
• Observe general installation and safety regulations for working on electrical
systems.
• Generally, you may not modify or convert the product.
2.6 Product-specific safety instructions
If for certain work to be carried out safety features on the product are temporarily
not used for functional reasons, you have to ensure the same safety and protection
level in a different way in accordance with valid regulations.

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WARNING
Hazardous movements!
Risk of injury due to incorrect activation of the proportional pressure reducing valve
via the analog amplifier module and resulting unforeseeable machine movements.
▶ Operate the amplifier only together with the valves specified in the type code.
▶ Observe safety in accordance with EN 13849 or IEC 62061.
▶ If persons have to enter the hazard zone while the control is active, provide
superordinate monitoring functions or measurers for personal safety. The plant
manufacturer/user has to rate and dimension these measures on the basis of
a risk and failure analysis according to the specific situation on site. The safety
regulations valid for the system have to be taken into account for this.
▶ The electronics emits interference to other electronics within the permitted limit
values. This can cause malfunction in the control process. Only use electronics
below the EMC limit values or provide appropriate shielding.
▶ The electronics of the analog amplifier module VT-MRMA1 responds to
electromagnetic interference from non-shielded, improperly installed or wrongly
connected signal cables. If the limit values given in the data sheet are exceeded,
malfunction or uncontrolled movements are possible. Adhere to the limit values
given in the data sheet, use only electronics below the EMC limit values or
provide proper shielding.
▶ Electrostatic processes, an inadequate grounding concept or missing
equipotential bonding can lead to damage to the electronics and hence
cause malfunction or uncontrolled movements of the machine. Ensure proper
grounding and provide equipotential bonding.
▶ Using the product outside the specified IP protection class can result in
short-circuit and malfunction and hence in uncontrolled machine movements.
Therefore, use the product only within the IP protection class and in
environments as specified in the data sheet.
▶ Provide safety functions for personal safety separately. The analog amplifier
module VT-MRMA1 itself does not include safety functions for personal safety
and is no safety-related component.
High electric voltage through incorrect connection!
Danger to life, risk of injury due to electric shock.
▶ When carrying out any work, disconnect the relevant machine section from the
power supply and protect it against being switched on again.
▶ Only connect devices, electrical components and lines which feature protective
extra low voltage (PELV) to connections or terminals having voltages from 0 to
50 Volt.
▶ Only connect voltages and power circuits that feature safe isolation from
dangerous voltages. Safe electrical isolation can be achieved with, for example,
isolating transformers, safe opto-couplers or mains-free battery operation.

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WARNING
Lightning!
Risk of uncontrolled machine movements.
▶ An inadequate grounding concept or missing equipotential bonding can lead to
damage to the electronics. Provide for equipotential bonding of the device.
Failures and defects in the control current circuits or the energy supply!
Risk of uncontrolled machine movements.
▶ Observe safety in accordance with EN 13849 or IEC 62061.
CAUTION
Hot surfaces!
Risk of burning.
▶ System parts can heat up during operation. Let system parts cool down before
touching it or wear protective gloves.
3 General notes on damage to material and
the product
The warranty is valid exclusively for the configuration delivered.
• Warranty claims will be rejected in the case of improper installation,
commissioning and operation as well as in the case of use not in accordance with
the intended purpose and/or improper handling.
NOTICE
High voltage!
Risk of damage to the analog amplifier module.
▶ Wire the analog amplifier module only when disconnected from the power
supply.
Overloading!
Risk of overloading and damage to the supply cable in the case of insufficient
dimensioning and/or operation with several electrical devices.
▶ Provide current limitation by overload protection.
▶ Select an appropriate rating of power supply unit and cables.
Short-circuit!
Risk of overloading and damage of the supply cable in the case of defects of the
electrical device.
▶ Provide current limitation by overload protection.
Impermissible temperature range!
Risk of overheating. The device can be thermally destroyed.
▶ Adhere to the specification in the data sheet.

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4 Scope of delivery
The scope of delivery includes:
• Analog amplifier module
Accessories such as cables and mains adaptor and cable sets are not included
in the scope of delivery, but have to be ordered separately. See also chapter 7.3
“Recommended accessories“on page 26.

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5 About this product
5.1 Performance description
The analog amplifier module VT-MRMA1-1 is used for controlling a DC motor-
actuated pressure reducing valve with self-locking feature. It is designed as module.
• Module housing for toolless quick “snap-in” installation
• Plug-in screw connectors that can be withdrawn individually
• Configurable pressure command value input with cable break detection feature (0
to 10 V, can be switched over to 4 to 20 mA)
• Separately adjustable ramp times for pressure command value input
• Actual valve position value with cable break detection feature and electronic limit
stops
• Position controller
• Characteristic curve correction for valve position command value
• Output stage with ”clocked control voltage” for the valve actuator
• 24 V inputs/outputs for operational states (enable, ready for operation, position
command value reached)
• Configurable actual pressure value input 0.5 to 5 V (can be switched over to 4 to
20mA) with cable break detection feature
• Integrated pressure switch function with adjustable switching thresholds
• Two 24 V outputs for pressure switches
• Test jack can be switched over
• Reverse polarity protection for power supply (short-circuit-proof power supply
unit)
• Power supply unit with DC/DC converter
• LED indicator lamps
Features

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5.1.1 Block circuit diagram of the controller structure of the analog amplifier
module:
Fig. 1: Block circuit diagram of the controller structure of the analog amplifier module
From the external pressure command value, the pressure command value processor
generates both, the internal pressure command value and − according to the
valve characteristics − the internal valve position command value. The PI position
controller acquires the system deviation on the basis of the valve position command
value and the actual valve position value and generates from this the position
control output for the DC motor in the pressure reducing valve. An absolute position
transducer integrated in the valve provides the actual valve position. The integrated
pressure switch function compares the processed actual pressure value with the
processed pressure command value. Pressure values above or below limit values can
be diagnosed via outputs A or B of the pressure switch.
5.2 Product description
5.2.1 Components that can be connected
The following components are to be connected to the analog amplifier module (for
data sheets, see chapter 1.2 “Required and supplementary documentation“ on page
5):
• ZDRS 6VP-1X: Proportional pressure reducing valve with electromotive adjustment
element (and optional pressure transducer). The valve is self-locking.
• HM20-2X: Pressure transducer at ZDRS 6VP-1X
• VT-NE30-2X: Power supply unit
• Machine control: command value provision, I/O for control and status of the
amplifier module
−
+
A
B
Pressure
command
value
Actual
pressure
value
Actual
pressure value
preparation
Pressure switch
function with adjustable
switching thresholds for
pressure command value
Pressure command value preparation
Internal
valve
position
command
value
Position control varialbe Actual pressure
value
PI
position
con
troller
Output
stage
Valve
Motor
Position
transducer
Actual position
value feedback
Actual
position value
preparation
Internal actual
valve position
command value
Internal pressure
command value

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Bosch Rexroth AG, VT-MRMA1-1, RE 30214-B/03.2019
Fig. 2: Proportional pressure reducing valve of type (Z)DRS, size 6, series 1X
1 Position transducer 2 Actuator
3 Main stage 4 Connection of pressure transducer
5 Pressure transducer
5.2.2 Function
The function of the analog amplifier module is described in data sheet 30214.
Fig. 3: Block circuit diagram of the amplifier module
12345
ready for operation
+ M
t<
xs=ws
wp ws
t< t>
t< t>
L0
M
PI U
U
U
U
U/I
U
U/I
U
2
B
signal v
0 V
54
- M
xs
13
+ senso
r
- senso
r
A
-wp
+wp
enable
-xp
+xp
powe
r
supply
L0 (0V)
5
6
7
1
2
12
11
wp
xp
xs
ws
t>
+ 7.5
V
- 7.5 V
M0
Zp
xp
Gp
EN
Gw
Z
w
S1.7-1.8
S1.1-1.6
xs
EN
Zx
Gx
S2.1-2.9
L0
L0
10
9
16
15
8
4
3
13
14
DC
DC
1
2
3
11
9
14
7
8
5, 6
4
3
2
10
12
15
13
1
0
4
5
1 Pressure command value preparation 2 Pressure command value feedforward
3 Ramp generator 4 Pressure command value attenuator
5 Linearization of valve characteristic curve 6 Amplitude limiter
7 Valve position controller 8 Fault detection
9 "Position command value reached" recognition 10 Output stage
11 Enable function 12 Actual valve position value acquisition
13 Actual pressure value preparation 14 Pressure switch function
15 Measuring point changeover switch

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5.2.3 Functions within the amplifier module
Pressure command value preparation takes places at various levels:
• Analog pressure command value provision with adjustable zero point correction
(current or voltage interface)
• Ramp generator for pressure increase or pressure reduction of the pressure
command value
• Pressure command value attenuator
• Linearization for compensating for the non-linear valve characteristic curve through
generation of the relevant valve position command value
• Amplitude limitation of the valve position command value
The result of command value preparation is the internal pressure command value
and the internal valve position command value.
Table 6: Pressure command value feedforward
Purpose Effect Setting
The pressure command value
feedforward generates the
internal pressure command
value signal from an external
pressure command value
signal taking account of zero
point compensation (zero
point potentiometer).
Pressure increase/reduction as
the pressure command value
becomes higher/lower.
Configure input with DIL
switch S1 to “0 to 10 V
differential input” or “4 to
20mA current input“. Zero
point potentiometer ZW: 30 %
When using the differential input (pressure command value) always activate or
deactivate both inputs simultaneously.
Make sure that the ground of the pressure command value (-wP, terminal 5) has
the same potential as the ground (L0, terminal 11) of the power supply unit (if
required, use an equipotential bonding strip to suppress disturbance more
effectively).
For carrying out zero point compensation using zero point potentiometer ZW,
potentiometer GWmust not be turned to the left-hand limit stop (= 0 %).
If the current input is not connected or in the event of a command value cable
break, the resulting internal pressure command value signal is < 0 %. In any case,
the valve comes to a standstill at its current position. When the enable is not set,
the valve cannot be adjusted, positioning control is inactive, but the positioning
signal (”command value reached”) and the pressure switch are active. The pressure
command value has therefore also to be applied when the enable signal is missing.
Table 7: Ramp generator
Purpose Effect Setting
Limits the increase in the
pressure command value input
signal.
A given step-change signal is
turned into a ramp-shaped
output signal.
Separate potentiometers t<
and t> for the ramp times of
pressure increase or pressure
reduction. The ramp time
refers to a signal change of
100 %.
The ramp time is not extended or reduced by the downstream ”pressure
command value attenuator”.
Command value
preparation (1)
Pressure command value
feedforward (2)
Ramp generator (3)

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The current ramp time can be established according to the following formula from
the voltage of the measuring signals (switch position 4 or 5) at test jack v (front):
The following table shows the value measured at the test jack and the associated
current ramp time:
Table 8: Ramp times
Table 9: Pressure command value attenuator
Purpose Effect Setting
Limits the maximum actual
pressure value
The internal pressure
command value is influenced.
With potentiometer GW: 0 %
to 130 %
Example: Application with pressure stage having a nominal value of 100 bar
A voltage applied by the machine control corresponds to 10 V (= 100 %) at input wp.
A max. pressure of 80 bar (= 80 %) is to be possible. Potentiometer Gw is used to
adjust the internal pressure command value to a voltage of 8 V (= 80 %) (voltage at
test jack vwith switch position 0). With an applied pressure command value of 10 V,
this corresponds to an actual pressure value of 80 bar.
Table 10: Linearization
Purpose Effect Setting
Compensation of a non-linear
valve characteristic curve
Generates the valve position
command value from the
pressure command value
None
Table 11: Linearization
Purpose Effect Setting
Internal limitation of the valve
position command value
(irrespective of the pressure
command value applied).
Safety limitation of the valve
stroke to +110 % and -5 %
None
5.2.4 Controller and functions closely related to the controller
The description refers to functions that are directly or indirectly related to the
position controller in functional terms.
Table 12: Valve position controller
Purpose Effect Setting
Generation of output variable
for clocked output stage
from the system deviation of
position.
Matching of the actual
valve position value with
the internally applied valve
position command value.
None
t = • 1 [sec]
1 V
Ut
Value at test jack position
4, 5
Utin Volt 10 5 3 2 1 0.5 0.01 0.05 0.03 0.02 0.01
Current ramp time (±20 %) t in sec 0.1 0.2 0.33 0.5 1 2 10 20 33.3 50 100
Pressure command value
attenuator (4)
Linearization of valve
characteristic curve (5)
Amplitude limiter (6)
Valve position controller
(7)

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Table 13: Output stage
Purpose Effect Setting
Generates the clocked control
voltage for the DC motor,
which acts as actuator in the
pressure reducing valve.
The DC motor adjusts the pilot
pressure by way of the position
of the spring plate. From this
pilot pressure, the main stage
of the pressure reducing valve
generates the reduced “actual
pressure value” by shifting the
valve spool.
None
The output stage output is short-circuit-proof. Moreover, the output stage is
de-energized when no enable is present or a fault has been detected.
Table 14: Enable function
Purpose Effect Setting
Activation of the position
controller and the output
stage.
Enables the valve adjustment
or pressure adjustment.
Enable signal by machine
control. Indication of enable:
Yellow LED on front panel
Enable input (terminal 7): When a voltage of less than +6 V is applied, the output
stage is blocked independently of the current position command value and actual
position value. The valve remains in the self-locked position. When a voltage greater
than +8.5 V is applied, positioning control and the output stage are activated. An
enable cable break corresponds to a 0 V signal.
When the enable is not set, adjusting the valve is impossible, positioning control
is inactive, but the positioning signal (”position command value reached”) and the
pressure switch are active. The pressure command value therefore also has to be
applied when the enable signal is missing.
▶ Make sure that the enable signal is only given when a new actuating process
of the valve is going to take place. When the new working pressure has been
reached, the enable has to be reset (see also application example in chapter 8.4,
on page 41)!
5.2.5 Actual value preparation
Actual value preparation refers to the closed-loop-controlled actual valve position
value, the resulting actual pressure value and the pressure switch function.
Table 15: Actual valve value acquisition
Purpose Effect Setting
Processing of the actual valve
position value of the position
transducer.
Generates the internal actual
position value signal for the
position controller.
With zero point potentiometer
Zx and sensitivity
potentiometer Gx.
Zx: 15 %
Gx: 90 % to 120 %
The position transducer integrated in the valve is supplied from a voltage output
(terminals 3 and 4). A cable break of a position transducer port is detected (ready
output) and the output stage is switched off.
Output stage (10)
Enable function "external
enable“ (11)
Actual valve position value
acquisition (12)

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Table 16: Actual pressure value input
Purpose Effect Setting
Generates the internal actual
pressure value signal from
the external actual pressure
value signal of the pressure
transducer.
Provision of the internal actual
pressure value signal for the
pressure switch function.
Configuration of the input
with DIL switch S1 to “0.5 to
5 V differential input” or “4 to
20mA current input“.
Zero point potentiometer ZP:
± 5 %
Sensitivity potentiometer
GP: 90 % to 120 %
When the actual pressure value input is configured as ”4 to 20 mA” input and
operated in series connection with a further, separate, external current input
(PLC, etc.), the module electronics provides an offset current at terminal 1. This
has to be taken into account when the external current input is calibrated!
• Monitoring of the actual pressure value input (depending on the characteristics of
the pressure transducer electronics):
• Cable break of the actual pressure value cables connected to the input (terminals 1
and 2)
• Exchange of the actual pressure value cables
• Cable break of the positive supply cable of the pressure transducer
• Cable break of the negative supply cable (ground) of the pressure transducer
• Detection of undervoltage at terminal 2 (+xp < 0.35 V)
If one of the faults above is detected, both pressure signals A and B drop to 0 V and
the red LED ”!” on the front panel of the amplifier module lights up.
In the event of a cable break of the actual pressure value cable, the further
operation of the closed-loop valve position control is not affected.
Table 17: Pressure switch function
Purpose Effect Setting
Uses switching thresholds A
and Bto monitor, whether the
actual pressure value signal is
within a window around the
pressure command value.
Actual pressure value
permitted only within the valid
range within the switching
thresholds. In the event of a
cable break or a value that
exceeds or falls below the
switching thresholds, the
closed-loop position control
function is maintained. Action
required from higher-level
control.
DIL switch S2 for the
individual configuration of
the lower (A) and upper (B)
switching threshold. The actual
pressure value has to be within
this range.
Table 18: Operational states of pressure switch signals A and B:
Actual pressure value Pressure switch signal A
(terminal 13)
Pressure switch signal B
(terminal 14)
No switching threshold exceeded 24 V (HIGH) 24 V (HIGH)
Value fallen below lower switching
threshold (insufficient pressure)
0 V (LOW) 24 V (HIGH)
Actual pressure value input
(13)
Pressure switch function
(14)

About this product 19/52
RE 30214-B/03.2019, VT-MRMA1-1, Bosch Rexroth AG
Actual pressure value Pressure switch signal A
(terminal 13)
Pressure switch signal B
(terminal 14)
Upper switching threshold exceeded
(excessive pressure)
24 V (HIGH) 0 V (LOW)
Cable break of actual pressure value
cables or pressure transducer supply
cables
0 V (LOW) 0 V (LOW)
Setting the pressure switch thresholds:
The upper and lower switching thresholds each are composed of a relative and an
absolute amount. The relative switching threshold is defined in % and refers to the
currently set pressure command value. The absolute switching threshold is defined
in % and refers to the nominal value (= maximum pressure) of the selected pressure
level (see figure below):
Fig. 4: Pressure switch thresholds
Overlapping (p1, p2) of the relative and the corresponding absolute switching
thresholds results in an envelope curve in the form of a ”funnel” (see figure above).
As long as the actual pressure value remains within the ”funnel limits” at a given
pressure command value, both pressure switch signals A and B are HIGH. If the
pressure exceeds or falls below one of the two limits (actual pressure value is in the
gray area), the corresponding pressure switch signals falls to LOW.
5.2.6 Monitoring functions
The monitoring functions of the amplifier module are to detect faults in the system
and in the supply lines and to initiate appropriate measures in the event of a fault.
B = LOW
A = LOW
100 %
100
%
p2
p1
Upper relative switching threshold
(in % of current command value)
Upper absolute switching threshold (in %
of nominal value of the pressure level)
Ideal valve characteristic curve
Lower absolute switching threshold (in %
of nominal value of the pressure level)
Lower relative switching threshold
(in %of current command value)
Actual pressure value
Pressure command value

20/52 About this product
Bosch Rexroth AG, VT-MRMA1-1, RE 30214-B/03.2019
Table 19: Fault detection
Purpose Effect in the event of a fault Setting
Fault detection for certain
signal cables and internal
processes.
Output stage is deactivated.
“Ready-for-operation” output
is switched to 0 V and the
green LED on the front panel
goes out.
None
The fault detection function monitors:
• Cable break of the pressure command value cables
• Exchanged pressure command value cables
• Cable break of the position transducer connecting cables
• Short-circuit of the position transducer supply cable with L0
When a new pressure adjustment process is being initiated, the following faults are
detected via the protective motor circuit (see “Protective motor circuit“ below):
• Exchanged motor cables (positive feedback)
• Jamming of the valve actuator
• Cable break of motor cables
When no fault is present, the green LED for readiness for operation lights up on
the front panel and the ”ready-for-operation” output is connected to the 24 V
operating voltage.
After the fault was rectified, the electronics can be re-activated by resetting and
then setting the ”enable” again.
The protective motor circuit is an integral part of the fault detection feature (see
page 20).
Table 20: Protective motor circuit
Purpose Effect Setting
Ensures proper operation
of the valve actuator by
monitoring the time required
for adjusting the position.
When the max. permissible
adjustment time (max. 4 sec)
is exceeded, the output stage
is deactivated, the green
LED on the front panel of the
module goes out, and the
”ready-for-operation” output is
reset to 0 V.
None
Example of faults, in the case of which the protective motor circuit responds:
• Jamming of the valve actuator
• Positive feedback as a result of exchanged motor cables
• Motor cable break
The protective motor circuit detects these faults only when a new pressure
adjustment process is being initiated.
Fault detection (8)
Protective motor circuit