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How do I know the COM port number?

The COM port to which the USB converter is connected may also be displayed in Windows:

  1. Click with the right mouse button on the Windows start icon
  2. Select the Device Manager
  3. In the category "Ports (COM & LPT)" you will find the assigned COM port.

Do I have to connect power supply to the unit?

No, the auxiliary power for the programming is supplied via the interface cable. It should be noted however, that the output is not in function.

For the diagnosis of the measuring device when installed, the interface cable is also suitable.

Do I need administrator rights for DRAGOmodbus?

Administration rights are required during installation, as the USB driver is integrated into Windows at system level. The installation of the driver is only necessary once.

The call and operation of DRAGOmodbus does not require administration rights.

Do I need administrator rights for DRAGOset?

No, the program DRAGOset can also be started directly, no installation is necessary. The optional Installation will setup DRAGOset user friendly with one icon on the desktop.

When you install the USB driver, administration rights are required because the drivers are integrated at the system level in Windows. The driver installation is required only once.

Do I need an installation of DRAGOset?

No, start of the exe-file is sufficient. The installation copies only DRAGOset to your hard drive and set up a desktop icon.

Where can I get the current software version?

Here on this website you will always get the latest version of DRAGOmodbus. After the download, simply run the installer again. Your settings will be retained during the installation.
The current version of DRAGOmodbus is 1.4.2

Where can I get the latest software version?

Here on this website you can always get the latest version of DRAGOset. After downloading, simply replace the EXE file or call the installer again. Your settings will be retained during the installation.
The current version of DRAGOset is 3.10.0

Why does DRAGOset not found the device at an other USB port?

For each USB interface Windows put on a separate COM port. Therefore, make sure, if possible, the USB converter always be connected to the same USB port.

For a different USB interface of Windows, a new COM port number is assigned. Enter this new COM port setting in DRAGOset menu "Settings | Communications".

Only 3.1 mm DIN Rail per channel

With our two-channel DH 11000 passive isolators or the DN 26000 standard signal isolating amplifier from the 6 mm series, you only need 3.1 mm DIN-Rail per channel to accommodate over 300 isolation distances on a 1-metre DIN Rail.

What is meant by standard signals?

In an industrial environment measuring signals are frequently converted for conveyance via the power lines. The standard signals have a fixed maximum value and are therefore especially easy to continue processing. The inputs of programmable logic controllers (PLC) or process control systems are frequently dimensioned for these standard signals.

What is live-zero?

Live-zero raises the identification rate of a plant's failures and hence increases operating reliability. Here the measuring value zero is not transmitted as a standard signal of the variable zero; instead it obtains an offset. For current loops this offset is fixed at 4 mA.
If there is line breakage or the transmitter fails, the result is a signal at 0 mA, but because measuring starts at 4 mA, the failure or line breakage can be detected unmistakably.

Customary live-zero standard signals are:

  • 4 - 20 mA
  • 2 - 10 mA
  • 2 - 10 V
  • 1 - 5 V

Don't I require any supply voltage?

No, the loop-powered isolator draws its auxiliary energy from the measuring circuit. The magnitude of the drop in voltage in the measuring circuit is to be found in the technical data.

Can I adapt the measuring range of the measuring transducer to my application?

The temperature measuring transducer of the High Functionality series gives you the option of using the DIP switches to adapt the beginning of measurement and its scope and the ZERO and SPAN potentiometers to your application.

The measuring transformers in the favourably-priced Tiny Snap series have to forego setting elements owing to the small structural size, so please specify your measuring range when ordering the measuring transformers. You will find an order code for the type range in the data sheet.

Is the output temperature or resistance linear?

The temperature-measuring transducers linearise the temperature characteristic of the connected sensor. A Pt 100 / Pt 1000 sensor changes its resistance with the temperature. However, the change is not linear over the temperature range, which means that without linearisation a crooked characteristic curve would result.

The built-in linearisation means that a measuring signal is made available on the output, which changes proportional to the temperature.

To what extent can I override the measuring range?

Within certain bounds the measuring range between, for example 4 and 20 mA can be exceeded or undercut. Normally a range from 3.8 to 20.5 mA should be able to reach the maximum output level. This is what NAMUR defines in its recommendation NE 43. Below and above these values there are voltage ranges for signalisations, typically 3.6 mA or 22 mA.

What is meant by auxiliary energy?

Auxiliary energy is the energy required to operate the device. In many cases auxiliary voltage is also called supply voltage or operating voltage.

In the case of loop-powered isolators the energy required is gained from the input signal (4 - 20 mA).

What is 3-port isolation?

3-port isolation comprises isolation distances between the input circuit and the output circuit and auxiliary energy. The supply of auxiliary energy is neither located on the input potential nor on the output potential; it is an independent galvanically-separated circuit.

The structure of the isolation amplifier with 3-port isolation affords reliable protection against erroneous measurements owing to earth problems and parasitic voltages.

What does the voltage drop at the input signify?

A loop-powered isolator, also known as a passive isolation amplifier, takes its supply from the input current. In order to take energy from the input current, the input causes a drop in voltage. The magnitude of the necessary drop in voltage is specified in the data sheet of the isolator.

What is a passive transmitter repeater?

A passive transmitter repeater comprises an input for a 4 … 20 mA transmitter signal from a measuring transducer with a 2-conductor system. The measuring transducer obtains its entire supply via this 2-wire circuit.

The output is connected to the process control or a PLC at 4 … 20 mA. The passive transmitter repeater requires no additional voltage supply because the auxiliary energy is obtained from the feeder circuit without the results becoming falsified.

How large is the hysteresis, or can it be adjusted?

A hysteresis describes the distance from the switching-on and cutting-off points in relation to the input parameter. Hysterisis prevents constant short switching-on and cutting-off operations caused by an unsettled input or measured value. If hysteresis is configured appropriately it is referred to as two-point-control.

In the case of our monitoring modules the switching point and the hysteresis can be adapted to your requirements by means of one 12-turn potentiometer each.

How do I configure the desired measuring range?

Our universal isolation amplifiers can cover a multitude of measuring ranges. To enable you to select your desired measuring range, these amplifiers have a row of small switches (DIP switches); the interaction between input and output are defined by how they are combined.

You will find a table with the feasible switch combinations on the type plate or on the other side of the isolator. Set all the switches marked with a dot in the table to ON.

What is meant by MTBF?

The MTBF, the average time until a failure occurs (MeanTime Between Failures), is a measure for the frequency with which the components fail. The greater the time, the longer is the period until a potential failure takes place.
There are two known standards for determining the MTBF value: the Siemens standard SN 29500 (2000/2004) and the military standard, MIL-217F, notice 2.

The device components used are assessed according to defined criteria for both of the standards. Depending on the mechanical structure and the load values, so-called FIT values are defined in the circuitry for each component. All the FIT values added together give the total FIT, which is then converted into hours or years and stated as the MTBF.

For example, our type DN 1012 loop-powered isolator has an MTBF of 1597.0 years according to the Siemens standard.

Can the isolation amplifier supply a transmitter?

Yes, a transmitter repeater or transmitter repetition amplifier can supply the 2 or 3-wire transmitter with energy by galvanically isolated means.

A 2-wire measuring transducer takes its voltage supply from the measuring signal, the current for which is provided by the transmitter repeater. In the case of 3-wire measuring transducers an additional input terminal with feeding voltage is available to the transmitter.

What do we adjust with zero/span potentiometers?

Errors and signal distortion, which may arise from sensor errors and/or varying measurements by the measuring transducer, are easy to compensate using the potentiometers on the front of the isolation amplifier.

For example, the input signals may contain a slightly falsified measured value. Using the potentiometers to compensate the ZERO and SPAN measured distance, this kind of divergence in the percent range can be corrected, enabling the downstream devices, e.g. a PLC to obtain a correct measured value.

How many contacts are available to me?

Two switching outputs are available in each of the DG monitoring modules. The two outputs can be configured separately. The switching point and the switching hysteresis can be configured at the front of the device using a 12-turn potentiometer. The switching status is displayed by a yellow LED on the front of the housing.

The effective direction and mode of operation can be switched by using the DIP switches. Both switching outputs can configured as MIN or MAX alarms.

The relay contacts switch high-output loads, optionally as N/O contacts or N/C contacts.

What is safe isolation?

Safe isolation is the mutual isolation of electrical circuits. This separation can be created by means of double insulation, basic insulation with an additional electric protection shield or reinforced insulation.

Safe isolation to protect maintenance personnel and the downstream devices against inadmissibly high voltage is described in the EN 61140 standard.

What is a passive isolation amplifier?

A passive isolation amplifier is an amplifier which requires no additional supply lines. These loop-powered isolators take their supply from the standard signal at the input.

Is it possible to electrically isolate HART transmitters?

Yes, when using the HART DC 52500, a 2-wire measuring transducer can be fed and operated by means of HART communication. The 4 - 20 mA measured value with the modulated HART signal is conveyed smoothly over the isolating distance; HART communication is bi-directional, i.e. it is transported in both directions across the electrical isolation.

Can I also isolate ac voltage?

Yes, but it depends entirely on the critical frequency of the isolation amplifier. A.c. voltages below the critical frequency specified on the data sheet can be transmitted by potentially isolated means. With some device types the critical frequency can be changed over using a DIP switch.

Are active switching states displayed?

Yes, the current switching state is indicated by a yellow LED at the front of the device.

The effective direction and mode of operation can be switched by using the DIP switches. Both switching outputs can be configured as MIN or MAX alarms. The relay contacts switch high-output loads, optionally as N/O contacts or N/C contacts.

How high is the test voltage?

The test voltage for the individual devices is specified in the technical data. In most cases the test voltage for DRAGO signal converters is between 1.5 kV and 2.5 kV (at 50 Hz, all circuits in against each other).

In the High Functionality series we also offer select types of loop-powered isolators, standard signal, multipurpose and shunt isolation amplifiers with 4 kV test voltage.

What is 4-port isolation?

The standard signal splitter splits the input signal and makes it available at 2 outputs. Hence the splitter consists of 4 mutually potentially-isolated units, an input area, two output areas and the area for the supply of auxiliary energy to the device.

4-port isolation separates these circuits galvanically from one another, thus providing reliable protection from erroneous measurements owing to earth problems and parasitic voltages.

Modbus RTU Protocol

The DMB devices implement the Modbus RTU Protocol. The Modbus protocol is a single master protocol. Therefore a slave only sends answer messages to former requests of the Modbus master device. The Modbus RTU standard defines a binary communication inside the Modbus Frame.


A Modbus RTU message frame consists of the following parts:

Modbus Frame

The 4 fields have the following meaning:

  • 1. Address Field: States the address of the slave that is addressed in the actual communication. The master itself has no address. The address 0 is reserved for broadcast communication. The addresses 248 to 255 are actually reserved by the Modbus standard.
  • 2. Function Code: A 1 Byte field that contains the command the slave has to process. The function codes are standardized for all Modbus devices. The DMB devices implement only a limited subset of function codes, depending on the devices.
  • 3. Data: This field contents the information referring to the function code (e.g. the address of a requested register). The data needed for each function code can be found in the specifications.
  • 4. CRC: The last field contains the two bytes of the CRC used to verify the data frame.


A start or an end of a Modbus RTU frame is indicated by a 3.5 Byte long pause which means that no devices on the network sends data.

What is meant by HART Communication?

Hart Communication is a standardized method of additionally transferring bi-directional communication on an analog measuring value. The modulation and the data log are defined exactly in the specifications of the HART Communication Foundation (

This is an FSK signal which is modulated in the measuring transducer to the measuring value, 4 - 20 mA output current of the transmitter. A HART modem is installed in the process controller; it transports the transmitted digital data to a process computer.

The great advantage of this concept is that the analog measured value can be evaluated conventionally. Furthermore, but without any additional cabling work, all kinds of information such as measured values, configuration data or set parameters can be made available to the user in digital form.

What is meant by a universal power pack?

Our Universal power packs in the High Functionality series for 20 - 253 V AC/DC can be used worldwide in all power supply networks. The high degree of efficiency largely prevents the device from heating up. This is reflected in excellent reliability and long-term stability.

Potential isolation towards the PLC

Frequently PLC inputs are not adequately potentially isolated. In this case it is feasible to install an isolation amplifier upstream from the input in order to clearly isolate the measuring signal.

Connecting the fill-level measuring transducer to a PLC

Measuring transducers, especially 2-wire measuring transducers often have the measuring signal available as current in the 4 to 20 mA range. However, for the analog input card of a PLC, input voltages are required within the 0 to 10 V range or 0 to 5 V.

Ideally, a standard signal isolation amplifier complements your system in two ways at once:

  • The isolation amplifier converts the current-measuring signal into the appropriate voltage signal
  • Thanks to the isolation amplifier you additionally have the galvanic isolation of the inputs

Do I have to readjust it after range switching?

No, the DRAGO Automation standard signal splitters can be switched in a calibrated state. All valid range combinations have already been compensated at the factory within the specified error margins.

RS485 Network for Modbus

The very common form of a Modbus network based on 2-wire RS485 is described detailed in "MODBUS over Serial Line - Specification and Implementation Guide V1.02". The RS485 is defined in the EIA-485 (meanwhile TIA-485) standard.

Below the only basic structure is described:


According to the Modbus Organization the devices are connected via 2 data lines and a third functional line:

  • D0   (which is referred to as “B” in the EIA/TIA-485)
  • D1   (which is referred to as “A” in EIA/TIA-485)
  • Common   (which is referred to as “C” in EIA/TIA-485)


The original RS485 standard allows 32 devices each with 1 so-called unit load. Modern devices offer a unit load which is only a fraction of 1 to enable more devices on the bus. The DMB devices have a unit load of 1/8 unit load (Rin ≥ 96 kΩ) to enable up to 256 devices in a RS485 network without the need for a repeater. This number is actually limited by the Modbus address space to 247.

The Resistors RT are used to minimize the reflections compared to an open ended line. The optimum value of the resistor depends on the wave impedance of the cable used. However a value of 120 Ω is a common choice.

The Polarization Network is needed to ensure proper potentials when none of the devices are sending and thus the lines D1 and D0 are floating. The value of RP depends on several things like bus load or termination resistors. The Modbus Organization suggests values from 450 Ω to 650 Ω for RP. The use of a polarization Network is strongly suggested to obtain a robust stable network. The polarization resistors are usually integrated in the master device.

Devices of the DRAGO DMB series don’t have internal resistors for termination or polarization.

What can I adjust with zero/span potentiometers?

Stray current in the measuring circuit causes signal distortion, which can be compensated easily with the ZERO potentiometer at the front of the isolation amplifier. Production tolerances of the shunt resistor can easily be corrected at the percent level using the SPAN-Poti, which means that, for example, an SPS obtains a correct measured value.

Can I connect up my 3-wire transmitter?

Yes, some of our transmitter repeaters have a terminal for the feeder voltage. So you can supply your transmitter from the feeder voltage and deliver the measuring signal to the transmitter repeater on separate terminals (the output current).

What does stating the burden data signify regarding amplifiers?

The burden specifies the degree to which the isolation amplifier may be loaded at the output without the measured value being falsified.

If there is one current output, the amplifier must provide output voltage, which - depending on the switched-on load - can make the current (measured value) flow. The maximum burden is calculated according to Ohm's law from the maximum output voltage at the current 20 mA output.
Example: the guaranteed maximum output voltage = 12 V is equivalent to a 600-Ohm burden.

With the voltage output it is exactly the same, only the output must be capable of delivering an appropriately high current so that the voltage (measured value) on the load can drop.
Example: guaranteed maximum output current = 20 mA, this means a permissible load of 2 kOhm.

Monitoring process variables

It is frequently expedient to additionally monitor measured process variables in the form of standard signals with additional alarm contacts in order to be able to report a plant failure.

You can monitor industrial standard signals with the alarm units from DRAGO Automation. You have 2 limit values available to you, which can be configured for the switching point and the hysteresis. The relay contacts switch high-output loads, optionally as N/O contacts or N/C contacts.

Saving installation costs

Costs are saved thanks to low installation expense. Simply connect a loop-powered isolator in between in current signals which you wish to isolate. Since no extra supply is required, no additional wiring or provision of auxiliary energy is necessary.

Comparison of measuring distances with potentiometers

Errors and signal distortion, which may arise from sensor errors and/or divergent measurements by the measuring transducer, are easy to compensate using the potentiometers on the front of the isolation amplifier.

For example, based on the installation geometry, sensors can deliver a slightly falsified measured value. Using the potentiometers to compensate the ZERO and SPAN measured distances, this kind of divergence in the percent range can be corrected, enabling the downstream devices, e.g. a PLC to obtain a correct measured value.

Connection via In-Rail-Bus

The primary way to connect the DMB devices is the rear In-Rail-Bus connector (A-E). Third-party devices without the In-Rail-Connector can be connected by an In-Rail-Bus Power-Terminals (order-no.: DZU 1401; DZU 1402). Some DMB devices also internally connect the Modbus signals to the terminals 5, 6 and 8. An overview of all connections on the enclosure is shown below:

Connections of DRAGO DMB devices

RS485 (Modbus) signal name In-Rail-Bus connector Optional Modbus terminals
D1 (A) A 5
D0 (B) B 6


Is the shunt resistor installed in the isolation amplifier?

No, the shunt voltage is tapped directly on the shunt and directed to the input of the shunt isolation amplifier. The input areas of our shunt isolator are aligned with the commercial shunt voltages.

Strong currents to be measured are directed via shunt resistors in order to measure the drop in voltage there. The comparatively low voltage at the shunt is tapped directly on the shunt and directed to the input of the shunt isolation amplifier using the 4-pole technique (also known as Kelvin connections or Kelvin contacting).

Monitoring of the electrical energy supply

Current and voltage alarm units from DRAGO Automation are available for monitoring currents and voltages in supply networks.

Measuring ranges of 1 or 5 A for the current alarm unit and 24, 48, 120 or 250 V for the voltage alarm monitor can be monitored by means of 2 limit contacts. With this you can implement a pre-alarm warning and a main alarm or achieve a MIN / MAX alarm signal.

The relay contacts switch high output, optionally as N/O contacts or N/C contacts.

Reuse of the measuring signal

You use the standard signal splitter to split the standard signal into 2 signals. This enables you to direct the measuring signal to different downstream devices without any retroactive effects and without mutual interference.


  • A measuring transducer delivers the 4 - 20 mA input current
  • Output I is configured for 4 - 20 mA and transmits the measured value to the process control
  • Output II is configured for 0 - 20 mA and controls a regulator

Transmitter supplied from the isolation amplifier

Our transmitter repeaters supply the feeder voltage for your transmitter.

2-wire transmitters regulate their own power consumption proportionate to the measured value; here the 4 - 20 mA connection provides the auxiliary energy for the transmitter and the level of the current is at the same time the output measured value.

3-wire transmitters usually have an active current output for the measured value and additionally terminals for the supply voltage (auxiliary energy).

Motor monitoring by means of a tachogenerator

A typical application for our universal isolation amplifier with bipolar input is motor monitoring with the aid of a tachogenerator.

The tachogenerator supplies output voltage proportionate to the drive speed. Depending on the direction of rotation, this voltage can be positive or negative, i.e. bipolar. This is how the actual value of the speed is determined, especially in the case of speed-controlled drives.

Conversion into another standard signal

Our standard signal isolation amplifiers support different standard signals at the input and output. With the aid of the small switches (DIP switches) you can configure the desired combination of input and output signal. A table showing the optional combinations is to be found on the type plate or on the label on the opposite side.

In the Tiny-Snap series you must specify the desired combination of input and output variables already at the time of ordering, because - owing to the small design no setting is offered on the amplifier.

Example: PC with USB to RS485 converter

Additional measuring option for process signals

The standard signal splitters from the High Functionality series can be configured as current or voltage outputs on the output side. This makes it possible to create a shunt for measuring the process variable in a 4 - 20 mA current loop using a 0 - 10 V scale. Without breaking the current loop, at output II you can observe the current measured value using a voltage indicator, a chart recorder or a DVM.

Image of the output load at the input

The loop-powered isolator conveys the input signal to the output without converting it, i.e. 4 mA appear as 4 mA at the out put and 20 mA appear as 20 mA at the output. The situation is similar regarding the burden on the output:

If I require an 8-volt burden voltage at the output, the input will also require 8 V plus the auxiliary power from the input circuit.

A shunt for measuring strong currents

Shunts are used to measure dc currents, especially in the case of high amperages. Voltage drops on the shunt proportionate to the current and is then connected to the input of a shunt isolation amplifier for further processing.

Shunts are typically manufactured in class 0.5 in compliance with DIN 43703 and are designed for rated currents in the range between 1 A and 15,000 A. The drop in voltage in the case of the rated current is stated to be 60 mV or 150 mV, depending on type.

HART Communication across the isolation distance

In addition to the analog 4…. 20 mA current signal, many 2-wire transmitters permit digital communication, which is modulated on the output current. A popular protocol is the Hart Communication of the HART Communication Foundation (

It is the function of an appropriate transmitter-repeater amplifier to also transmit the modulated frequency in unadulterated form across the isolation distance. In view of the fact that HART Communication must function in both directions, the HART transmitter repeater has a return channel which transmits the digital queries from the master to the slave (field device, transmitter) against the normal analog data flow.

Use in customised mechnical engineering

A universal isolation amplifier is especially good to use in customised mechanical engineering with all its individual measuring functions. The many input and output ranges and the universal long-distance power pack make it possible to use just one type of device in numerous applications thanks to many possible signal combinations.

Our DK 8000 special signal isolation amplifier, which can process other unipolar and bipolar input and output signals is available in different versions for isolating and converting customer-specific special signals.

Do you have further questions?

Then ask us your question by email or call our hotline at +49 30 40 998-222.