WO2016180499A1

WO2016180499A1 - Galvanically isolated current transmitter with self-adjustment on recognition of operating conditions

Info

Publication number: WO2016180499A1
Application number: PCT/EP2015/060950
Authority: WO
Inventors: Carlo Gattanini
Original assignee: Pepperl and Fuchs SE
Current assignee: Pepperl and Fuchs SE
Priority date: 2015-05-12
Filing date: 2015-05-19
Publication date: 2016-11-17
Anticipated expiration: 2017-11-12
Also published as: EP3093720B1; EP3093720A1

Abstract

The invention is directed to a connection module (101) for a galvanically isolated connection of field devices (134, 136, 148, 152) to a control facility, comprising a primary side (110) with primary connections for the connection to the control facility, a secondary side (111) with secondary connections for the connection to the field device and coupling means (103) for operationally connecting the primary side to the secondary side and galvanically isolating the primary side from the secondary side. The connection module is characterized in that electronic detecting and adjusting means are provided for automatically detecting properties and/or requirements, particularly electrical signal properties and/or electrical signal requirements, of a control facility and a field device when the control facility is connected to the primary side and the field device is connected to the secondary side and both, the control facility and the field device, are operative and for automatically adjusting electrical parameters, in particular the electrical transfer characteristics, of the connection module to comply with detected properties and/or requirements of the control facility and the field device. The invention is furthermore directed to a method for a establishing a galvanically isolated connection of a field device to a control facility.

Description

Galvanically isolated current transmitter with self-adjustment on recognition of operating conditions The invention relates to a connection module according to the preamble of claim 1 and to a method for establishing a galvanically isolated connection of field devices to a control facility according to the preamble of claim 19.

More specifically, the present invention relates to a device for providing intrinsically safe supply, controlling and/or evaluation of field devices in explosion-protected are- as. Such devices are known and usually have a current transformer for providing a galvanic isolation between a control and the hazardous area.

A general challenge in this context consists in providing different barrier functionalities for, in each case, different field devices. One solution in the prior art resides in using, in each case, different barrier circuits for the field devices. This, however, proved to be expansive and prone to malfunction.

Furthermore, apparatuses are known in the prior art where the functionalities of multifunctional l/O-boards are configured by microcontrollers or similar intelligent devices. Such setups which include software, however, can give to rise to difficulties with regard to safety standards. A connection module for a galvanically isolated connection of field devices to a control facility according to the preamble of claim 1 comprises a primary side with primary connections for the connection to the control facility, a secondary side with secondary connections for the connection to the field device and coupling means for operationally connecting the primary side to the secondary side and galvanically isolat- ing the primary side from the secondary side.

Such a connection module is e.g. described in WO 2013 1 10 296 A1 . Therein, a device for the intrinsically safe supply, control and/or evaluation of field devices in the explosion-proof area is described which comprises a current transmitter for providing galvanic separation between a control and the explosion-proof area, connections on the control side for connection to a control device and a first and a second connection on the field side for the connection to field devices to be connected, wherein the second connection on the field side is configured to supply, control and/or evaluate field devices with analog functionality together with the first connection on the field side. The device is characterized in that the second connection on the field side is configured to supply, control and/or evaluate field devices with digital input functionality together with the first connection on the field side, a third connection on the field side that is configured to supply field devices with digital output functionality together with the first connection on the field side is provided, and signal determination means for activating and or determining a functionality of the second and/or the third connection on the field side are provided.

WO 2013 1 10 295 A1 describes an apparatus for the intrinsically safe supplying, trig- gering, and/or evaluation of field devices in the explosion-proof realm, comprising terminals at the controller end which are to be connected to a bus and to a voltage supply, terminals at the field device end which are to be connected to the field devices, and a plurality of intrinsically safe voltage supplies, each of which has different characteristic values. The described apparatus is characterized in that signal defining means are provided to define different functionalities for at least one intrinsically safe pair of the terminals at the field device end.

WO 2013 1 10 294 A1 describes a connection module for field devices in the explosion-proof realm, comprising a housing that has a plurality of terminals at the controller end which are to be connected to at least one input/output module as well as ter- minals at the field device end which are to be connected to the field devices. The connection module described is characterized in that the housing includes different resistors which are hard-wired to different terminals at the field device end and/or to terminals at the controller end in order to provide intrinsically safe pairs of terminals at the field device end which have different characteristic values. The object of the present invention may be seen in providing an improved device, i.e. an improved connection module for field devices, especially for application in the explosion-proof realm.

This object of the present invention is solved by connection module having the fea- tures of claim 1 and by a method having the features of claim 19. Advantageous embodiments of the present invention are subjects of dependent claims and are described in the following, in particular with reference to the attached figures.

According to the invention, the connection module as described above is characterized in that electronic detecting and adjusting means are provided for automatically detecting properties and/or requirements, particularly electrical signal properties and/or electrical signal requirements, of a control facility and a field device when the control facility is connected to the primary side and the field device is connected to the secondary side and both, the control facility and the field device, are operative and for automatically adjusting electrical parameters, in particular the electrical trans- fer characteristics, of the connection module to comply with detected properties and/or requirements of the control facility and the field device.

In connection with the specification of the present invention, the term properties of a field device shall be understood to designate all kinds of properties of such a field device, especially signal properties, which may be detected by observing or measur- ing electrical characteristics (or responses to stimuli) of such a field device. Important examples of such properties may be resistance, inductance, voltage or current output, and other kinds of characteristics. The term requirements, especially signal requirements, of a field device shall be understood to designate all kinds of requirements which have to be compiled with in order to allow for an intended or designated use of such a field device. Important examples of such requirements may be maximal or minimal voltages and/or currents as well as voltage and/or current offsets, accuracy and transfer characteristics.

Variable kinds of field devices and different control devices can therefore be connected to the connection module according to the invention. The connection module according to the invention can therefore be used as a universal intrinsically safe con- nection module. Specialized types of connection modules, which are individualized for each different field device and the stockpiling of which is expensive are therefore no longer necessary.

In principle, the galvanically isolated coupling can be brought about by optocouplers, i.e. the coupling means can comprise optocoupling means. According to a preferred embodiment of the present invention, however, the coupling means comprises at least one current transformer with a primary and a secondary winding for galvanic isolation, with a primary current flowing through the primary winding and a secondary current flowing through the secondary winding. In principle, the transformer can have any suitable transformation ratio. Preferably, the transformer has a 1/1 transformation ratio. Thereby, the design of the connection circuit can be simplified. Preferably, the transformer is driven as a current repeater.

According to a preferred embodiment of the present invention, the coupling means comprise a DC/AC-AC/DC converter. Such components are known in the art. Generally, it is possible to realise certain functions of the connection module according to the invention by making use of intelligent devices like, e.g., microcontrollers. I.e. the electronic detecting and adjusting means can comprise a microcontroller for automatically adjusting electrical parameters, in particular the electrical transfer characteristics, of the connection module to comply with detected properties and/or re- quirements of the control facility and the field device.

A very important advantage of the invention, however, resides in the fact that, contrary to solutions of the prior art, it can in principle be realised without any programmable devices like microcontrollers or microprocessors. Using analog comparators instead of a digital microprocessors increases the security and reliability of connection modules according to the present invention if compared to connection modules comprising digital microprocessors. This is particularly important in view of the qualification for safety standards.

According to a further preferred embodiment of the present invention, the electronic detecting and adjusting means can comprise a primary current measurement device for measuring a primary current, in particular a current through the primary winding, and/or the electronic detecting and adjusting means can comprise a first variable resistor which is connected in series to the primary connections and/or the first variable resistor can be adjusted in dependence of a primary current measured by the primary current measurement device. This is useful if the primary current gives a hint to the type of field device being connected to the connection module.

A further preferred embodiment is characterized in that the electronic detecting and adjusting means comprise a primary voltage measurement device for measuring a voltage at the primary side, in particular a voltage across the primary winding and more preferably a voltage present at one connection of the primary winding, and/or that the first variable resistor is adjusted also in dependence of a voltage measured by the primary voltage measurement device. A further preferred embodiment is characterized in that the electronic detecting and adjusting means comprise a secondary voltage measurement device for measuring a voltage at the secondary side, in particular a voltage across the secondary winding, that the electronic detecting and adjusting means comprise a second variable resistor which is connected in series to the secondary connections, in particular in series to the secondary winding, and that the second variable resistor is adjusted in dependence of a voltage measured by the secondary voltage measurement device. These embodiments are especially useful if the primary and/or secondary voltage gives a hint to the type of field device being connected to the connection module.

A further preferred embodiment is characterized in that the primary current measurement device, the primary voltage measurement device and/or the secondary voltage measurement device comprise analog comparators and that a measured primary current is compared with at least one primary current theshold, a measured primary voltage is compared with at least one primary voltage theshold, and/or a measured secondary voltage is compared with at least one secondary voltage theshold.

A further preferred embodiment is characterized in that the electronic detecting and adjusting means are configured to adjust electrical parameters of the connection module to comply with properties and requirements of a field device being controlled by an analog signal, outputted by the secondary connections, if the primary current exceeds a first primary current threshold value, preferably given by 3.5 mA, and if, in particular simultaneously, the primary voltage is smaller than a first primary voltage threshold value, preferably given by 21 .5 V.

A further preferred embodiment is characterized in that the electronic detecting and adjusting means comprise a current offset means for applying a current offset to the primary side current and that the current offset means applies a current offset to the primary current in the case where a measured primary current exceeds the first primary current threshold and, in particular simultaneously, a measured primary voltage is smaller than the first primary voltage threshold. A further preferred embodiment is characterized in that the electronic detecting and adjusting means comprises means for increasing a parallel capacitance at the primary side, means for reducing a series impedance of a primary low pass filter and/or means for reducing the dead-time of a driver for the 1 /1 -transformer.

A further preferred embodiment is characterized in that the electronic detecting and adjusting means are configured to adjust electrical parameters of the connection module to comply with properties and/or requirements of a field device being controlled by a digital signal, outputted at the secondary connections, if the primary current exceeds a second primary current threshold value, preferably given by 24 mA, which exceeds the first current threshold. A further preferred embodiment is characterized in that the means for increasing a parallel capacitance at the primary side, the means for reducing a series impedance of a primary low pass filter and/or the means for reducing the dead-time of a driver for the 1/1 -transformer are operational when the measured primary side current exceeds a second current threshold, particularly 24 mA. A further preferred embodiment is characterized in that the electronic detecting and adjusting means are configured to adjust electrical parameters of the connection module to comply with properties and/or requirements of a field device producing a digital signal, e.g. a proximity switch, to be inputted into the secondary connections, if the primary current is smaller than a third primary current threshold value, preferably given by 0.1 mA, the third primary current threshold value being smaller than the first primary current threshold value.

A further preferred embodiment is characterized in that the electronic detecting and adjusting means are configured for proportionally reducing the primary voltage by means of the first variable resistor in the case when the primary side current is smaller than the third threshold, in particular 0.1 mA.

A further preferred embodiment is characterized in that monitoring means are provided for monitoring at least one of a primary current, a primary voltage and/or a secondary voltage. Such a monitoring means can be helpful for achieving the desired Safety Integrity Level (SIL) in both, analog and microcontroller based embodiments.

A further preferred embodiment is characterized in that the the electronic detecting and adjusting means is configured to recognise a line breakage in the secondary connections with a field device if the primary current is smaller than a fourth primary current threshold value, preferably given by 0.1 mA, which is smaller than the first primary current threshold. This feature may facilitate detection of a line breakage in the connections with a field device, possibly in connection with the evaluation of other indicating criteria.

According to a preferred embodiment of the present invention, the connection module is configured to be able to report a recognized line breakage in the connections with a field device to the control facility. This feature may facilitate the report of a line breakage in the connections with a field device, possibly in connection with further means for communication.

The method for a establishing a galvanically isolated connection of field devices to a control facility according to the present invention comprises the following steps: con- necting a control facility to primary connections at a primary side of a connection module and connecting a field device to secondary connections at a secondary side of the connection module. According to the invention, properties and/or requirements, particularly electrical signal properties and/or electrical signal requirements, of the control facility and the field device are detected when both, the control facility and the field device, are operative and electrical parameters, in particular the electrical transfer characteristics, of the connection module are adjusted to comply with detected properties and/or requirements of the control facility and the field device.

According to a preferred embodiment of the present invention, this method uses a connection module according to the present invention.

Advantageous embodiments of the present invention will be described in more detail in connection with the following figures below:

Fig. 1 shows a schematic representation of the basic circuitry of a preferred embodiment of a connection module according to the present invention; Fig. 2 shows a schematic representation of further circuitry of a preferred embodiment of a connection module according to the present invention.

Fig. 3 shows a schematic representation of a current-voltage diagram representing the characteristics of a preferred embodiment of a connection module according to the present invention. Figure 1 shows a connection module 101 according to the present invention which, through terminals 1 17 and 1 18, can be connected to a circuit of a control facility on the control side. The connection circuit to the control side is preferably designed to be compatible with the input and/or output of a universal or a configurable input/output system and preferably comprises a micro-controller or micro-processor. Such connection circuits are known in the prior art.

Terminals 1 19 and 120 constitute a power input of the connection module 101 , which is used to provide auxiliary power to the connection module, if required. The power is transmitted via a galvanic isolation 1 12 of the power supply, preferably a transformer plus a rectifier plus a chopper, via connection 1 16 to the DC-side 104 of a DC/AC- AC/DC-converter 104, 106, which converts a DC input applied at terminal 1 17 via diode 1 13 and connection 1 14 into an AC signal, provided by the AC-side 106 of the DC/AC-AC/DC-converter 104, 106 to the secondary winding 108 of the current transformer 108, 103, 109, preferably via a fuse 153, e.g. a 100 mA fuse. Terminal 1 18 is connected to the galvanic isolation 1 12 of the power supply via a connection 1 15. Apart from galvanic isolation, the booster 1 12 preferably also serves to adjust signal waveforms by balancing nonlinearities of the transformers.

The current transformer 108, 103, 109 separates the control side or primary side 1 10 of the connection module 101 from the field side or secondary side 1 1 1 of the connection module. Both sides are therefore galvanically isolated from each other.

The DC/AC-AC/DC-converter 104, 106 may preferably be operated in both directions, i.e. converting a DC input applied at terminal 1 17 via diode 1 13 and connection 1 14 into an AC signal, as well as converting an AC signal applied at the AC- side 106 of the DC/AC-AC/DC-converter 104, 106 into an DC signal, available at the DC-side 104 of the DC/AC-AC/DC-converter 104, 106.

The secondary winding 109 of the current transformer 108, 103, 109 is connected to the AC-side 105 of a DC/AC-AC/DC-converter 105, 107, which converts the AC- current flowing through the secondary winding 109 into a DC-signal, which is then available at the DC-side 107 of the DC/AC-AC/DC-converter 105, 107. The DC/AC- AC/DC-converter 105, 107 may preferably be operated in both directions, i.e. converting an DC input applied at terminals 129, 130, 131 or 132 through the connections 121 and 122 to the DC-side 107 of DC/AC-AC/DC-converter 105, 107 into an AC signal, then available at the AC-side 105 of the DC/AC-AC/DC- converter 105, 107 and then flowing through the secondary winding 109, as well as converting an AC signal applied at the AC-side 105 of the DC/AC-AC/DC- converter 105, 107 into an DC signal, then available at the DC-side 107 of the DC/AC-AC/DC-converter 105, 107.

Any DC-signal applied to or provided by the DC-side 107 of the DC/AC-AC/DC- converter 105, 107 via connections 121 and 122 will pass the circuitry connecting the DC-side 107 of the DC/AC-AC/DC-converter 105, 107 with the terminals 129, 130, 131 and 132, this circuitry comprising the diode 126, the Zener diodes 123, 124 and 125 as well as the resistors 127 and 128 as depicted in figure 1 . As shown in figure 1 , various field devices may be connected to the terminals 129, 130, 131 and 132 on the field side of the connection module.

First, a measurement device for a physical quantity like, e.g. temperature, pressure etc., which acts as a current source 134 can be connected to terminals 132 and 131 through connections 133 and 135. The current source 134 sources a variable current, e.g. in the range of 0 / 4 to 20mA, in dependence of the measured physical quantity. Furthermore, a measurement device for a physical quantity like, e.g. temperature, pressure etc., which acts as a current sink 136 can be connected to terminals 131 and 129 through connections 135 and 137. The current sink 136 sinks a variable current, e.g. in the range of 0 / 4 to 20mA, in dependence of the measured physical quantity. When either current source 134 or current sink 136 is connected to the connection module terminals 132 and 131 or 131 and 129, respectively, the connection module works in an "analog input" mode, because, in each case, an analog signal is input to the connection module either by sourcing (field device = current source 143) or by sinking (field device = current sink 136) a variable current. The transferred signals, i.e. the variable currents, are preferably in the range of 0 (minimum) to 4 ... 20 mA (maximum).

Alternatively, a field device 148 expecting an analog input signal through connections 138 and 139, connected to terminals 131 and 129, respectively, may be con- nected to the connection module, which in this case works in an "analog output" mode, because the connection module outputs an analog signal to the analog field device 148. Examples for such devices 148 are e.g. electrical drives or actuators or various kinds.

The connection module may also be used to output a digital signal to a field de- vice 149 through connections 140 and 141 , connected to terminals 131 and 129, respectively. An example for such a field device 149 is e.g. a valve or an actuator of any kind which has only two states (like "open" or "closed").

Digital devices 150, 151 or 152, switch 152 preferably being a NAMUR-switch, generating digital output signals may also be connected via connections 142, 143, 144, 145, 146 or 147 and terminals 131 and 129 to the connection module. The connection module will recognize the required mode at any time and be able to transmit these signals between the control facility and the field device in both directions through the galvanic isolation 108, 103 and 109.

In Figs. 1 and 2, similar and equivalent components generally carry the similar refer- ence numerals. More specifically, the corresponding reference numerals have, in each case, the same first and second digits. E.g. connectors 129,..,132 in Fig. 1 are the same components as connectors 229, ..,232 in Fig. 2. Such components are generally described only once.

As shown in figure 2, the DC/AC-AC/DC-converter 104, 106 may be realized by a series of two pairs of switches 265, 266, controlled by a full bridge driver 269. Depending on the switch positions, potentials at conductors 273 and 274 will be "high" or "low", with a resulting current flowing through winding 208. The direction of this current is also defined by the switch positions. A voltage drop along shunt resistor 267, preferably a 5 Ohm resistor, which is proportional to this current, will cause the input of operational amplifier 270 to vary between various voltage levels, generating a signal 271 , an amplified primary current, which influences the first voltage controlled resistor 261 via operational amplifier 262 together with the primary voltage measured at point 264, which is amplified by operational amplifier 260. One purpose of this first voltage controlled resistor is to modulate the drop between the output of the distributed control system and the primary side of the transformer 208, 203 and 209. The signal provided by operational amplifier 270 at 271 also influences a step-down output of a galvanically isolated power supply 212. The step-down can amount e.g. to 9 Volts.

Another operational amplifier 275 is provided between connection 221 and the sec- ond voltage controlled resistor 276. Both voltage controlled resistors, 261 and 276, are designed to keep a minimum primary voltage at point 264 of preferably 21V and a low impedance to comply with the requirements of the Highway Addressable Remote Transducer (HART) communication protocol, which is widely used in connection with field devices. A voltage of 24 V is preferably applied to the power supply input 219 and 220. The diagram of figure 3 illustrates the different domains in a two-dimensional space spanned by the primary voltage U (given in Volt) and the primary current I (given in mA), which correspond to different operating modes of corresponding preferred embodiments of the connection device. The threshold values should be taken as exam- pies only. Domain C1 corresponds to the operating mode, in which the connection module is configured to adjust its electrical parameters to comply with properties and/or requirements of a field device being controlled by an analog signal, outputted by or inputted to the connection module, if the primary current exceeds a first current threshold value, preferably given by 3.5 mA, and if the primary voltage is smaller than a first voltage threshold value, preferably given by 21 .5 V.

Domain C2, which partially overlaps with C1 , corresponds to the operating mode, in which the connection module is configured to adjust its electrical parameters to comply with properties and/or requirements of a field device being controlled by a digital signal, outputted by the connection module, if the primary current exceeds a second current threshold value, preferably given by 24 mA.

Domain C3 corresponds to the operating mode, in which the connection module is configured to adjust its electrical parameters to comply with properties and/or requirements of a field device producing a digital signal, to be inputted in the connection module, and/or is configured to be able to recognize a line breakage in the con- nections with a field device, if the primary current is smaller than a third current threshold value, preferably given by 1 mA.

The following list of reference numerals and symbols is an integral part of the specification.

List of reference numerals and symbols

101 device according to the present invention, current transmitter

103 current transformer

104 DC-side of DC/AC-AC/DC-converter on the control side

105 AC-side of DC/AC-AC/DC-converter on the field side

106 AC-side of DC/AC-AC/DC-converter on the control side

107 DC-side of DC/AC-AC/DC-converter on the field side

108 control side (primary) winding of current transformer

109 field side (secondary) winding of current transformer

1 10 control side = primary side

1 1 1 field side = secondary side

1 12 galvanically isolated power supply of the device according to the present invention

1 13 diode for reverse polarity protection

1 14 connection between diode 1 13 and DC-side of DC/AC-AC/DC-converter on the control side

1 15 connection between terminal 1 18 and galvanically isolated power supply 1 12

1 16 connection between DC-side of DC/AC-AC/DC-converter 104 and galvanically isolated power supply 1 12

1 17 terminal on the control side

1 18 terminal on the control side

1 19 terminal on the control side

120 terminal on the control side

121 first connection between field side circuitry of the device and DC-side 107 of

DC/AC-AC/DC-converter

122 second connection between field side circuitry of the device and DC-side 107 of DC/AC-AC/DC-converter

123 Zener diode

124 Zener diode

125 Zener diode

126 diode 127 resistor

128 resistor

129 terminal on the field side

130 terminal on the field side

131 terminal on the field side

132 terminal on the field side

133 connection of current source

134 current source

135 connection

136 field device producing analog signals

137 connection

138 connection

139 connection

140 connection

141 connection

142 connection

143 connection

144 connection

145 connection

146 connection

147 connection

148 field device receiving analog signals

149 field device receiving digital signals, e.g. valve

150 field device producing digital signals, e.g. mechanical switch 151 field device producing digital signals, e.g. mechanical switch

152 field device producing digital signals, e.g. NAMUR switch

203 current transformer

205 AC-side of DC/AC-AC/DC-converter on the field side

207 DC-side of DC/AC-AC/DC-converter on the field side 208 control side winding of current transformer

209 field side winding of current transformer

212 galvanically isolated power supply 213 diode

214 connection between diode 1 13 and DC-side of DC/AC-AC/DC-converter on the control side

215 connection between terminal 218 and galvanically isolated power supply 212 216 connection between DC-side of DC/AC-AC/DC-converter 204 and galvanically isolated power supply 212

217 terminal on the control side

218 terminal on the control side

219 terminal on the control side

220 terminal on the control side

221 first connection between field side circuitry of the device and DC-side of DC/AC-AC/DC-converter 207

222 second connection between field side circuitry of the device and DC-side of DC/AC-AC/DC-converter 207

223 Zener diode

224 Zener diode

225 Zener diode

226 diode

227 resistor

228 resistor

229 terminal on the field side

230 terminal on the field side

231 terminal on the field side

232 terminal on the field side

260 operational amplifier

261 variable resistor

262 operational amplifier

264 connection

265 pair of switches

266 pair of switches

267 resistor

268 ground 269 full bridge driver, driving the switches 265 and 266

270 operational amplifier

271 connection

272 step-down 9V output

273 connection

274 connection

275 operational amplifier

276 variable resistor

U[V] primary voltage in volt

l[mA] primary current in ampere

C1 area of case 1

C2 area of case 2

C3 area of case 3

Claims

1 . Connection module (101 ) for a galvanically isolated connection of field devices to a control facility, comprising

a primary side (1 10) with primary connections (1 17, 1 18; 217, 218) for the connection to the control facility,

a secondary side (1 1 1 ) with secondary connections (129,..,132; 229, ..,232) for the connection to the field device (134, 136, 148, ..,152) and

coupling means (103,..,109) for operationally connecting the primary side (1 10) to the secondary side (1 1 1 ) and galvanically isolating the primary side (1 10) from the secondary side (1 1 1 ),

characterized in that

electronic detecting and adjusting means (260, 261 , 262, 270, 275, 276) are provided for

automatically detecting properties and/or requirements, particularly electrical signal properties and/or electrical signal requirements, of a control facility and a field device when the control facility is connected to the primary side (1 10) and the field device is connected to the secondary side (1 1 1 ) and both, the control facility and the field device, are operative

and for automatically adjusting electrical parameters, in particular the electrical transfer characteristics, of the connection module to comply with detected properties and/or requirements of the control facility and the field device.

2. Connection module according to claim 1 ,

characterized in

that the coupling means comprises at least one current transformer (103, 108, 109) with a primary (108) and a secondary (109) winding for galvanic isolation, with a primary current flowing through the primary winding and a secondary current flowing through the secondary winding.

Connection module according to claim 2,

characterized in that

the transformer (103, 108, 109) has a 1/1 transformation ratio.

Connection module according to one of the claims 1 to 3,

characterized in

that the coupling means (103, ..,109) comprise a DC/AC-AC/DC converter.

Connection module according to one of the claims 1 to 4,

characterized in

that the electronic detecting and adjusting means comprise a primary current measurement device (267, 270) for measuring a primary current, in particular a current through the primary winding (208),

that the electronic detecting and adjusting means comprise a first variable resistor (261 ) which is connected in series to the primary connections (217, 218) and

that the first variable resistor (261 ) is adjusted in dependence of a primary current measured by the primary current measurement device (267, 270).

Connection module according to claim 5,

characterized in

that the electronic detecting and adjusting means comprise a primary voltage measurement device (260) for measuring a voltage at the primary side (1 10), in particular a voltage across the primary winding (208) and more preferably a voltage present at one connection (264) of the primary winding (208), and that the first variable resistor (261 ) is adjusted also in dependence of a voltage measured by the primary voltage measurement device (260).

Connection module according to one of the claims 1 to 6,

characterized in

that the electronic detecting and adjusting means comprise a secondary voltage measurement device (275) for measuring a voltage at the secondary side (1 1 1 ), in particular a voltage across the secondary winding (209), that the electronic detecting and adjusting means comprise a second variable resistor (276) which is connected in series to the secondary connections (229,..,232), in particular in series to the secondary winding (209), and that the second variable resistor (276) is adjusted in dependence of a voltage measured by the secondary voltage measurement device (275).

Connection module according to one of the claim 5 to 7,

characterized in that

that the primary current measurement device (267, 270), the primary voltage measurement device (260) and/or the secondary voltage measurement device (275) comprise analog comparators and that

a measured primary current is compared with at least one primary current theshold,

a measured primary voltage is compared with at least one primary voltage theshold, and/or

a measured secondary voltage is compared with at least one secondary voltage theshold.

Connection module according to one of the claims 5 to 8,

characterized in that

the electronic detecting and adjusting means are configured to adjust electrical parameters of the connection module to comply with properties and requirements of a field device being controlled by an analog signal, outputted by the secondary connections, if the primary current exceeds a first primary current threshold value, preferably given by 3.5 mA, and if, in particular simultaneously, the primary voltage is smaller than a first primary voltage threshold value, preferably given by 21 .5 V.

10. Connection module according to one of the claims 5 to 9,

characterized in

that the electronic detecting and adjusting means comprise a current offset means for applying a current offset to the primary side current and

that the current offset means applies a current offset to the primary current in the case where a measured primary current exceeds the first primary current threshold and, in particular simultaneously, a measured primary voltage is smaller than the first primary voltage threshold.

1 1 . Connection module according to one of the claims 1 to 10,

characterized in

that the electronic detecting and adjusting means comprises

means for increasing a parallel capacitance at the primary side,

means for reducing a series impedance of a primary low pass filter and/or means for reducing the dead-time of a driver for the 1 /1 -transformer.

Connection module according to one of claims 5 to 1 1 ,

characterized in that

the electronic detecting and adjusting means are configured to adjust electrical parameters of the connection module to comply with properties and/or requirements of a field device being controlled by a digital signal, outputted at the secondary connections, if the primary current exceeds a second primary current threshold value, preferably given by 24 mA, which exceeds the first current threshold.

Connection module according to claim 1 1 or 12,

characterized in that

the means for increasing a parallel capacitance at the primary side,

the means for reducing a series impedance of a primary low pass filter and/or the means for reducing the dead-time of a driver for the 1/1 -transformer are operational when the measured primary side current exceeds a second current threshold, particularly 24 mA. 14. Connection module according to one of claims 5 to 13,

characterized in that

the electronic detecting and adjusting means are configured to adjust electrical parameters of the connection module to comply with properties and/or requirements of a field device producing a digital signal, e.g. a proximity switch, to be inputted into the secondary connections, if the primary current is smaller than a third primary current threshold value, preferably given by 0.1 mA, the third primary current threshold value being smaller than the first primary current threshold value. 15. Connection module according to claim 14,

characterized in that

the electronic detecting and adjusting means are configured for proportionally reducing the primary voltage by means of the first variable resistor (261 ) in the case when the primary side current is smaller than the third threshold, in par- ticular 0.1 mA.

Connection module according to one of claims 1 to 15,

characterized in that

the electronic detecting and adjusting means comprise a microcontroller for automatically adjusting electrical parameters, in particular the electrical transfer characteristics, of the connection module to comply with detected properties and/or requirements of the control facility and the field device.

Connection module according to one of claims 1 to 16,

characterized in that

monitoring means are provided for monitoring at least one of a primary current, a primary voltage and/or a secondary voltage. Connection module according to one of claims 5 to 17,

characterized in

that the the electronic detecting and adjusting means is configured to recognise a line breakage in the secondary connections with a field device if the primary current is smaller than a fourth primary current threshold value, preferably given by 0.1 mA, which is smaller than the first primary current threshold. 19. Method for a establishing a galvanically isolated connection of a field device to a control facility, comprising the following steps:

connecting a control facility to primary connections (1 17, 1 18; 217, 218) at a primary side (1 10) of a connection module (101 ) and

connecting a field device (134, 136, 148, ..,152) to secondary connec- tions (129, ..,132; 229, ..,232) at a secondary side (1 1 1 ) of the connection module (101 ) and

characterized in that

properties and/or requirements, particularly electrical signal properties and/or electrical signal requirements, of the control facility and the field device are de- tected when both, the control facility and the field device, are operative and that electrical parameters, in particular the electrical transfer characteristics, of the connection module are adjusted to comply with detected properties and/or requirements of the control facility and the field device. 20. Method according to claim 19

characterized in that

a connection module according to one of the claims 1 to 18 is used.