The invention relates to a connection module for process control systems for connecting transducers to • a control system, the connection module having junctions to accomplish a connection for supplying electric power and for carrying measuring signals between a connection cable attached to the module and the transducers to be connected to the module.

Generally, when various processes are being automati¬ zed, a special connection box, which can be opened, is used between the control cabinet and the transducers, all connections being made thereto by opening the connection box and joining the transducer conductor terminals by screw joints to a correct location on a terminal block. Signals are carried from the terminal block to the control cabinet through a connection cable.

Making connections for separate transducers is difficult and time consuming. Moreover, connections can go wrong, for example the supply voltage for the transducer may be connected to a wrong conductor, which can result in a measuring failure and, in the worst case, in breakdown of the transducer. Another problem has been the protection of the connection from humidity.

The object of the invention is to remove the drawbacks mentioned above. To achieve this the connection module according to the invention is mainly characterized in that the module comprises a circuit board in a casing, the circuit board having connections to accomplish the above mentioned connection, the connections being made to the connection cable on one hand and, on the other hand, to bayonet sockets on the outside surface of the casing, operating on the plug-in principle,,

the transducer cable terminals to be connected to the connection module having plugs fitting into the sockets.

The advantage of this system is the fact that the electric power supply to the transducers and the control signal from the transducers to the control system can be always connected quickly and correctly.

The circuit board can be fixed to the module by casting so that the cast material at the same time covers the circuit board. In this way, protection from humidity is obtained for the connections and components and, at the same time, a firm structure is obtained for the module.

Moreover, the form of the bayonet sockets and plugs can be arranged so that they can be connected to each other only in such a position that the terminals supplying electric power and the terminals transmitting the signal are brought face to face.

The invention will be described in the following referring to the enclosed drawing in which

Figure 1 shows a connection module and the transducers connected thereto according to the invention, and

Figure 2 shows an alternative embodiment of the connection module.

The connection module 1 has a plastic casing la having a circuit board inside marked with a dashed line 2 in the drawing. The casing can be opened, for example by opening the screws which clamp the casing halves together. However, this is not necessary since the casing need not be opened when the module is in use.

The circuit board is in communication with the connection cable 3, which is attached to the casing 1 and by which the module can be connected to the control system, for example to a control cabinet. The circuit board includes the necessary connections and components for conducting the electric power supply, like transducer control voltage, carried by the connection cable 3, from the connection cable to the transducers and, on the other hand, to conduct the measuring signals from the transducers via the connection cable to the control system. The circuit board can have additional electrical components and circuits for processing measuring signals from the transducers.

The said connections are in contact with bayonet sockets 4 on the outside of the casing operating according to the plug-in principle. The terminals of the transducer cables 6 to be connected to the connection module are provided with plugs 5 fitting to the sockets. The drawing shows two transducer cables 6 of this kind connected to the connection module by means of plugs 5, the actual transducers being marked with the reference number 7 in the drawing. The transducers can, in this case, be so- called intelligent transducers comprising elements for performing the actual measurement and the electronics involved therein.

Both the bayonet sockets 4 and the plugs 5 are provided with terminals for the wire/wires effecting the power supply and the wire/wires transferring measuring signals. The bayonet sockets and the plugs 5 being inserted therein have been so formed that they can be connected with each other only in such a position where the terminals for the power supply and the terminals for the measuring signals are face to face. In this way, wrong connections can be prevented. In each socket-plug pair there are, for example, four

terminals, of which two or three may be operating and the fourth is e.g. for a line for error message.

Figure 2 shows one advantageous embodiment of the connection module as a longitudinal cross section. The connection module is so constructed that to the bottom of the casing, being open above, a circuit board 2 is inserted so that the components and circuits therein are facing up. These are in contact with the bayonet sockets 4 on the opposite side of the board which go through holes 8 in the bottom of the casing when the board is inserted in place. The end of the connection cable 3 is led through a hole 9 on the side of the casing, whereafter necessary connections can be made on the circuit board 2. After this casting material 10 can be cast on the board 2 covering the components and circuits and, at the same time, fixing the board 2 and the connection cable 3 firmly to the casing la. One can use as casting material a resin which hardens with a curing agent at room temperature and which does not damage electric circuits and components but which provides a very efficient protection against humidity. After the casting a cover can be placed on the casing if desired, but the hardened casting material can be left open. Thus, the casing 1 acts in a way as a casting mould.

The connection module can be provided with a suitable number of terminals for different transducers, and the terminals within the same module can be of different type for connecting different types of transducers to the control system. Moreover, several connection modules can be used in the process by means of which the transducers forming a specific subsystem of the whole can be connected to the cable between the connection module and the control system.