Tips & Tricks

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.

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

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.

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

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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:

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.

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.

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

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 R_T 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 R_P depends on several things like bus load or termination resistors. The Modbus Organization suggests values from 450 Ω to 650 Ω for R_P. 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.

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).

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.

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.

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).

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.

Example:

• 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

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.

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.

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 (www.fieldcommgroup.org/technologies/hart).

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.