GB2086587A - Electrical fluid pressure transducers - Google Patents

Abstract

In a fluid pressure transducer, particularly for differential pressure measurement, separating diaphragms 3,4, an overload protection device 2 and the actual transducing element 1, are accommodated each in a separate housing block namely the separating diaphragm block 7, the overload protection block 6 and the pressure transducing element block 5 which are detachably connected with one another in that sequence by bolts 8, 9. The overload protection device contains a bellows 30 made fast by a spring on two sides. The specification also describes transducers without overload protection devices, Figures 2 and 4 (not shown). <IMAGE>

Description

SPECIFICATION Measuring transducer for measuring pressure differences The invention relates to a measuring transducerfor measuring pressure differences which can be used in a plurality of technological installations, such as power stations, chemical plant and the like, for the measurement of process values which can be reduced to a pressure or a pressure difference, for controlling, regulating or monitoring these processes. Thus for example the process value ofthrough- flow of a liquid flowing through a conduit can be measured with the measuring transducer according to the invention as the pressure difference dropping over a measuring orifice, at high static pressure.

Measuring transducers are known which comprise a pressure transducer converting the measured pressure into an electric signal, which transducer can for example be a semi-conductor deformation body utilising the piezo-resistive effect and possessing integrated strain resistances, as described in DDR PS 133,714 of the Applicant. The pressure transducer is protected against contact with the measured medium by interposition of separating diaphragms, the pressure transmission from the measured medium to the transducer taking place through a non-compressible liquid, as for example silicon oil. Known pressure difference measuring transducers contain two chambers filled with noncompressible liquid in one housing block, which are closed off to the exterior by separating diaphragms and in the common housing partition of which the pressure transducer is secured as measuring element.The protection of the pressure transducer against unilateral overloading is often achieved in that the overloaded separating diaphragm can apply itself to the housing partition, the liquid hitherto situated between separating diaphragm and housing partition being displaced and received by an elastic element, for example a metal bellows, inserted likewise into the housing partition.

Measurement accuracy and zero point constancy of the measuring transducers are substantially dependent upon whether the deflection of the separating diaphragm at the commencement of operation can be kept very small, since every deflection of the separating diaphragm by reason of its inherent spring rate effects a pressure variation in the liquid and thus on the measuring element. In general therefore a very small and equal volume of the filled chambers is sought so that the variation of liquid volume occurring on temperature variations, and thus the separating diaphragm deflection with the effect of zero point deviation are small.

U.S.A. Patent Specification 4,028,945 describes an overload protection system of the stated kind in which the initially unstressed metal bellows inserted in the housing partition is secured by an initially stressed compression spring against deflection of the bellows bottom in both directions as far as an overload threshold, that is to say a pressure value fixed close above the end value of the measurement range. On account of the necessity of bilateral deflectability of the bellows the spring possesses a double clamping. It is clamped by a clamp with fixed distance connected with the bellows bottom and by a second clamp connected with the housing, likewise with fixed distance. It is disadvantageous that the clamp distance necessarily is affected by manufacturing tolerance, whereby the belllows and thus the separating diaphragms move.Furthermore the overlaod protection is not externally accessible in a simple manner, that is without extensive dismantlement of the measuring transducer, and is not adjustable. That however is desirable in order to provide the possibility in the production process of the measuring transducer of using one overload protection device for a series of types with different measurement ranges. Afurther disadvantage consists in that the pressure transducer, the overload protection device and the separating diaphragms are arranged in one housing block. Thus every temperature variation of the measurement medium is trans mitted fully to the entire liquid charge and thus brings the undesired diaphragm deflections in combination with a greater temperature error of the pressure transducer itself, since the latter too is subjected to the full temperature variation.

Afurther pressure difference measuring transducer is described in German Pub.Sp. 27,18931, where the pressure transducer is removed from the housing block in which the overload protection device and the separating diaphragm are arranged, and is connected with this block through capillary leads.

The disadvantage of this solution is that, by reason of the arrangement of the overload protection in the immediate vicinity of the separating diaphragms, a large proportion of the liquid volume is directly exposed to the temperature influence of the measured medium. Temperature fluctuations in the measured medium thus cause a great variation of volume of the liquid and thus an undesired movement of the separating diaphragms. The accessibility of the overload protection and its adjustment from the exterior are not possible. The capillary lead provided between the said housing block and the transducer, providing the high hydraulic resistance necessary for the necessary damping of pressure surges, renders difficult the operation of filling the measuring transducer with the pressure transmission liquid.

Afurther pressure difference measuring transducer is known from Ger.Pat.Sp. 2,819,303, which uses a separate separating diaphragm block containing special Invar blocks to compensate temperature influences. The separating diaphragm block is connected through appropriate passages with a second block in which there are arranged the overload protection device, using two initially stressed overload protection diaphragms, and the semi-conductor transducer. The volume capacity of such an overload protection diaphragm, already deformed in cap form by initial stress, is substantially lower in comparison with the volume capacity of the ordinarily used metal bellows or corrugated diaphragms of comparable size. Therefore temperature compensation blocks of Invar are provided additionally in the separating diaphragm block.By reason of the expan sion difference between housing and Invar blocks the gap spaces between the two enlarge on increase of temperature and receive a part of the likewise expanding liquid, so that even at higher operating temperatures the quantity of liquid expelled by the separating diaphragm in the case of overload and to be received by the overload protection diaphragm is kept small. Since the coefficient of thermal expansion of the pressure transmission liquid is substan tially greater than that of the housing and the filler bodies, for effective temperature compensation the dimensions of the housing must be relatively large, since the oil volume cannot be reduced at will.In order to keep the size of the housing and Invar bodies as small as possible nevertheless, the gap spaces between Invar bodies and housing must be very small (stated at 25.4 micrometres), so that the oil volume remains correspondingly low. Thus this solution necessarily leads to an increased expenditure of materials and manufacture for the measuring transfer.

Further disadvantages are to be seen in the fact that the desirable narrow gap between the Invar blocks and the inner wall of the housing considerably impedes the introduction of the pressure transmission liquid into the measuring transducer, and in that the temperature-controlled major gap width variation caused by operation makes the hydraulic resistance of the pressure communication between separating diaphragm and pressure transducer greatly temperature-dependent, whereby the dynamic properties of the measuring transducer, such as the time transmission behaviour and the damping of pressure pulses on the input side, become undesirably temperature-dependent.

In general it is an essential disadvantage in the known measuring transducers that in their style of construction they are directed to one particular, closely limited purpose, whereby the economical mass production of one appliance system with a plurality of different types, which becomes necessary by reason of many different operational conditions such as measurement ranges, pressure measurement or pressure difference measurement, overload protection necessary or unnecessary, chemical aggressivity of the measured medium, dynamics of the measure value variation and operational temperature, is disadvantageously influenced.

It is the aim of the invention to produce a measuring transducer forthe measurement of pressure differences which permits the economical manufacture of an appliance system of pressure difference and pressure-measuring transducers with a plurality of types, wherein the influences of the working temperature of the measured medium are kept low, the pressure transducer is protected securely against overloading by an externally accessible, adjustable overload protection device, without reduction of its accuracy of operation, the filling of the measuring transducers with the pressure transmission liquid is substantially facilitated and the passage crosssections in the separating diaphragm block are large and are reduced in size only after the operation of filling of the measuring transducer, and the dynamic transmission behaviour between separating diaphragm and pressure transducer is adaptable to the operational conditions in a simple manner.

It is the problem of the invention to produce a measuring transducer for the measurement of pressure differences in which the overload protection device is accommodated neither with the separating diaphragms nor with the transducer in a common housing block, while the passage cross-sections in the separating diaphragm block are large and are reduced in size only after the operation of filling of the measuring transducer and the liquid volume directly adjoining the medium is very small, so that the influence of the operating temperature of the measured medium is slight even without the provision of special temperature compensation blocks.

In accordance with the invention this problem is solved in that all three essential functional groups of the measuring transducer, the separating di aphragms, the overload protection device and the pressure transducer, are accommodated in separate housing blocks, the separating diaphragm block, the overload protection block and the pressure transducer block, and these are detachably connected with one another in the stated sequence.

In advantageous development of the invention the overload protection devices comprise a bellows made fast on two sides, known perse, the interior of the bellows forming a chamber which terminates outwards in a threaded opening which is closed in pressure-tight manner with a stopper. The bellows is initially stressed in both directions by a spring, the bellows bottom being firmly connected with a rod which has a projection which in common with a projection in the overload protection block forms the one support of the spring. An internally threaded bush screwed on to the rod connected with the bellows bottom, in common with an externally threaded bush screwed into the threaded opening of the overload protection block, forms the other support for the spring.After removal of the stopper closing the threaded opening it is possible in a simple manner to adjust the initial stress of the spring and thus the overload protection threshold by adjustment of the threaded bushes. Furthermore it is possible to achieve a precise, play-free spring seating by adjustment of one of the threaded bushes from the exterior of the completed measuring transducer.

In further advantageous development of the invention the essential part of the hydraulic resistance of each of the two pressure transmission passages is generated within the separating diaphragm block, that is to say in the section situated between the separating diaphragm and overload protection device. The separating diaphragm block for this purpose possesses two transmission passages which extend straight from the one side wall of the separating diaphragm block to the other side wall and are each in communication with the space between separating diaphragm and separating diaphragm carrier disc. The transmission passages are widened at the one side wall of the separating diaphragm block into a threaded opening which serves as filling opening for the introduction of the pressure transmission liquid and is closable with a ball and screw.The diameter of the transmission passages has a value of at least 3 mm., facilitating the introduction of the transmission liquid. The high hydraulic resistances necessary for the damping of pressure surges are generated in that after the filling operation, hydraulic resistance elements are pushed from the exterior into the transmission passages so that the cross-section effective for the pressure transmission is greatly reduced. Thus it is possible at any time to bring about specific variations in the dynamic behaviour of the measuring transducer by a variation of the hydraulic resistances, which is achieved simply by the insertion of hydraulic resistance elements with different diameters.

The hydraulic resistance elements pushed into the transmission passages are preferably of cylindrical formation and atthe end lying in the installed condition between the ball and the passage opening into the transmission passage, which brings about the connection with the space between separating diaphragm and diaphragm carrier disc they possess a greater diameter which by press fit or knurling ensures a firm seating in the transmission passage.

For easy withdrawal of the hydraulic resistance elements they possess an internal threading at the stated end. An advantageous further development of the invention consists on that the pressure transducer block is connected directly with the separating diaphragm block, the overload protection block being eliminated, so that for utilisation cases where such overload protection is unnecessary an economic adaptation of the measuring transducer is achieved by the elimination of the complete overload protection block.

Afurther modification of the measuring transducer consists in that on the low-pressure side of the measuring transducer the measuring chamber lid, separating diaphragm including carrier disc, transmission liquid and hydraulic resistance elements are omitted and the chamber hitherto closed off by the separating diaphragm on the minus side is connected with atmosphere, so that with the same components a pressure-measuring transducer is produced which is more secure against overload.

Another modification of the measuring transducer is achieved in that the overload protection block and, on the low-pressure side of the measuring transducer, the measuring chamber lid, separating diaphragm including carrier disc, transmission liquid and hydraulic resistance elements are omitted and thus with the same components a pressuremeasuring transducer is produced without overload protection.

The invention will be explained in greater detail below by reference to an example of embodiment. In the accompanying drawings: Figure 1 shows a cross-section through a pressure-difference measuring transducer in accordance with the invention with overload protection device, Figure 2 shows a cross-section through a pressure-difference measuring transducer without overload protection device, Figure 3 shows a cross-section for a pressuremeasuring transducer with overload protection device, Figure 4 shows a cross-section through a pressure-measuring transducer without overload protection device.

Figure 1 shows a pressure-difference measuring transducer according to the present invention in which the three essential functional elements of such a measuring transducer, namely the pressure transducer 1, the overload protection device 2 and the separating diaphragms 3 and 4 are accommodated each in their own housing block, the pressure transducer block 5, the overload protection block 6 and the separating diaphragm block 7, and are aligned with one another in the stated sequence and connected detachably with one another by connection elements 8 and 9.The separating diaphragm block 7 consists of a relatively flat square centre plate 10, on the side faces of which the separating diaphragms 3 and 4, which are each welded at the circumference with a carrier disc 11, are secured as replaceable construction units, and of two measuring chamber lids 12 and 13 which are fitted in sealing manner on the edges of the carrier discs 11 and form the high and low pressure chambers 14 and 15.

Two straight pressure transmission passages 16, 17 of about 3 mm. diameter extend through the centre plate 10 from the side wall 18 to the side wall 19 of the separating diaphragm block 7 and are widened at the side wall 19 to form a threaded opening 20 which serves as filling opening for the introduction of the transmission liquid 21 and is closable with a ball 22 and screw 23. The centre plate 10 further comprises two narrow pressure transmission passages 24 which constitute the connection between the chamber filled with transmission liquid 21 between separating diaphragm 3 or 4 and the corresponding carrier disc 11 and the pressure transmission passages 16 and 17 respectively.On the side wall 18 of the centre plate 10 there are further provided securing elements 25 for securing the pressure transducer block 5 with the separating diaphragm block 7 in a form of embodiment of the measuring transducer without overload protection device, according to Figures 2 and 4. Into the pressure transmission passages 16 and 17 there are pushed cylindrical hydraulic resistance elements 26 which have a larger diameter at the end nearerthe filling opening, ensuring a firm seating in the transmission passage by press fit 27 or knurling 28.

To facilitate withdrawal the hydraulic resistance elements have an internal threading 29. The large cross-section of the transmission passages 16, 17 considerably facilitates the operation of filling the measuring transducer with the transmission liquid 21. The requisite hydraulic resistance between the separating diaphragm and the overload protection device is produced by the fact that cylindrical hydraulic resistance elements are pushed into the transmission passages. Due to the fact that the pressure transmission in the passages 16 and 17 nowtakes place in an annular cross-section and thus the wetted surface is substantially larger than in a normal cylindrical passage, the hydraulic resistance is greater for the equal cross-sectional area.The accommodation of the greatest part of the hydraulic resistance in the space between the separating diaphragms 3 and 4 and the overload protection device 2 guarantees good damping of pressure surges already at the overload protection, so that the occurrence of pressure oscillations at the metal bellows 20 and thus also at the pressure transducer 1 is largely counteracted. It is possible to conform with different dynamic requirements of the measuring transducer in a simple way in that hydraulic resistance elements 26 with a different diameter are used.

The overload protection block 6 contains a metal bellows 30 which is made fast against axial deflection in both directions by an initially stressed spring 31. For this purpose the bellows bottom 32 is firmly connected with a rod 33 having a projection 34 which in common with a projection 35 in the housing block 36 forms the one support of the spring 31. The other support of the spring 31 is formed by an internally threaded bush 37 which is screwed on to the rod 33, and an externally threaded bush 38 which is screwed into the threaded opening 39 situated in the housing block 26.

When the stopper 40 is removed the initial stress of the spring 31 can be adjusted from the exterior by adjustment of one of the threaded bushes, the other threaded bush being correspondingly readjusted so that the two threaded bushes form a flat seating surface for the spring. Due to the fact that it is possible at any time from the exterior to realise the desired flat seating surface by adjustment of one of the threaded bushes, an idle play of the metal bellows 30 without spring stress is reliably prevented.The simple adjustment of the overload threshold on the overload protection device, possible from the exterior, brings the advantage in the production of the measuring transducer that an overload protection device can be used for a series of measuring transducer types with different measurement ranges, so that a smaller multiplicity of types of overload protection devices is required. The adjustment of the overload threshold, to be effected in dependence upon the pressure transducer utilised, can take place as described on the finishing measuring transducer.

In the housing block 36 there are provided pressure transmission passages 41 and 42, formed as narrower bores, which constitute the continuation of the pressure transmission passages 16 and 17 situated in the separating diaphragm block and produce the connection with the pressure transducer 1. The bellows interior with the space in which the springs 31 is situated forms a chamber 43 which terminates to the exterior in a threaded opening 39 and is closed in pressure-tight manner by the stopper 40. The passage 48, which is a component of the chamber 43, has a substantially lower hydraulic resistance than the passage 16 or 17. The bellows exteriorfo ms a second chamber 44.

The pressure transducer block 5 preferably contains a relatively rigid small semi-conductor diaphragm plate as pressure transducer 1, the construction of which is knownperse and described for example in DDR Patent Application 133,714. The feeding of the strain gauge elements, which in known manner form a bridge circuit, and the tapping of the electric output signal take place through thin wires which are connected with the terminal pins 45.

The terminal pins 45 are inserted in pressure-tight and electrically insulated manner in the wall of the pressure transducer block 5.

In Figure 2 there is illustrated an embodiment of a pressure-difference measuring transducer according to Figure 1 without overload protection 6. This form of embodiment is realised with the same components merely by omission of the overload protection block 6, the connecting element 9 and the gaskets 46, 47.

Figure 3 shows in further modification a pressuremeasuring transducer with overload protection device which is likewise realised with the same components as in Figure 1 in that the separating diaphragm block 7 is fitted on the minus side without measuring chamber lid 13, separating diaphragm 4, carrier disc 11, hydraulic resistance element 26 and transmission liquid 21, since these parts have no function in pressure measurement with the atmospheric air pressure as reference pressure.

A pressure-measuring transducer without overload protection is illustrated in Figure 4, being realised from the pressure-measuring transducer with overload protection device according to Figure 3 in that the overload protection block 6, the connecting element 9 and the gaskets 46,47 are omitted and the pressure transducer block 5 is connected by means of the securing element 8 and 25 directly with the separating diaphragm block 7.

The modifications as described above make it clear that the measuring transducer according to the invention permits the economic manufacture of an applicance system consisting of many types. Using the same components it is possible in a simple manner to realise pressure and pressure-difference measuring transducers either with or without overload protection. By the joining together of various separating diaphragm, overload protection and pressure transducer blocks it is possible to conform with the most various utilisation conditions with a minimum basic range of different components. Thus the numbers of the individual components are increased, the effectiveness of manufacture is improved and service is facilitated by the possibility of simple exchange of component groups.

The manner of operation of the measuring transducer according to the invention is described below as follows: Firstly the manner of operation of the pressuredifference measuring transducer with overload protection device according to Figure 1.

The pressure taken for example from the plus side of an effective pressure source is introduced into the measuring chamber 14 and transmitted by way of the separating diaphragm 3 to the transmission liquid 21 behind this separating diaphragm and thus through the pressure transmission passages 24, 16, 41 and the chamber 44 to the small semi-conductor diaphragm plate of the pressure transducer 1. Correspondingly the pressure tapped on the minus side on the effective pressure source is introduced into the low-pressure chamber 15 and acts through the separating diaphragm 4 upon the transmission liquid behind this separating diaphragm and thus through the pressure transmission passages 24, 17 and 42 and the chamber 43 upon the back of the semi-conductor diaphragm plate of the pressure transducer 1.The pressure difference occurring on the semi-conductor diaphragm causes a flexure of the latter which varies with the pressure difference, effecting in the strain gauge elements ofthe semiconductor diaphragm, which are sensitive to flexure stresses, a variation of resistance which is processed further into a proportional variation of the electric output signal of the measuring transducer.

If the pressure difference of the pressures introduced into the measuring chambers 14 and 15 exceeds the measurement range end value and thus the overload threshold of the overload protection device 2, set with the springs 31,then overloading exists. If the pressure 24 acting in the measuring chamber 14 on the plus side is too great, the separating diaphragm 3 applies itself to the correspondingly profiled face of the carrier disc 11 and thus prevents a further rise of the pressure on the far side of the separating diaphragm 3.When the separating diaphragm 3 is applied to the diaphragm carrier disc 11 the liquid volume situated between the latter and the diaphragm is displaced and flows into the chamber 44 formed by the bellows exterior, in which the bottom 32 of the metal bellows 30 acting as partition shifts, as soon as the force acting from the exterior upon it becomes greater than the initial stress force of the spring 31 set by means of the threaded bushes 37,38. From the thereby decreasing bellows interior, the chamber 43, the transmission liquid 21 flows through the bore 42 and the transmission passage 17 into the space between carrier disc 11 and separating diaphragm 4, which widens by deflection of the separating diaphragm 4.

During overloading the spring 31 is compressed more than illustrated, the one spring end then bearing only upon the externally threaded bush 38 and the other spring end bearing only the projection 34 of the rod 33. If the overload pressure drops again to values below the overload threshold, the spring 31 through the rod 33 presses the bottom 32 of the metal bellows 30 back again into the original position, which at the same time effects the corresponding conveying back of the transmission liquid 21.

In the case of overloading on the minus side the manner of operation is analogous. The separating diaphragm 4 applies itself to the carrier disc 11, the liquid volume thereby displaced flows into the bellows interior, the chamber 43, which enlarges due to stretching of the bellows, whereby liquid is displaced from the bellows exterior, the chamber 44, and forced beneath the separating diaphragm 3. The spring 31 is then compressed more than illustrated, the one spring end bearing only upon the internally threaded bush 37 and the other spring end bearing only upon the protection 35 of the housing block 36.

If the overload pressure drops again below the overload threshold, the spring 31 forces the deflected system into the original position again.

The appliance embodiment of a pressuredifference measuring transducer without overload protection device as illustrated in Figure 2 possesses within the normal working range the same manner of operation as the embodiment according to Figure 1. In the case of overload the semi-conductor diaphragm shatters when the bursting pressure is reached, and the separating diaphragm of the overloaded side applies itself to the carrier disc 11. The expelled transmission liquid flows through the corresponding pressure transmission passages and the shattered semi-conductor diaphragm into the space between the diaphragm and the carrier disc 11, which space enlarges by deflection of the separating diaphragm loaded with the low pressure.Since the separating diaphragms 3,4 do not lose their function capacity even under this overloading, no consequent damage occurs in the measuring transducer due to the measured medium. Restoration is thus effected merely by the replacement of the pressure transducer block 5 with the destroyed pressure transducer 1 and introduction of a new liquid charge 21.

The manner of operation of the pressuremeasuring transducer with overload protection device as shown in Figure 3 is as follows:- The measured pressure introduced into the measuring chamber 14 acts through the separating diaphragm 3 upon the transmission liquid 21 which transmits the measured pressure through the passages 24, 16, 41 and the chamber 44 to the semi-conductor diaphragm. Every variation of the measured pressure effects a corresponding variation of the electric output signal, as described with reference to Figure 1.

In the case of overload the overload protection device 2 acts as described with reference to Figure 1 for the case of overloading on the plus side.

The pressure-measuring transducer as shown in Figure 4 without overload protection device corresponds in its manner of operation to that of Figure 3, as long as the measured pressure lies in the normal working range. In the case of overload the semiconductor diaphragm breaks when the bursting pressure is exceeded, the separating diaphragm 3 coming into abutment and the displaced transmission liquid 21 flowing away through the pressure transmission passages and the broken semiconductor diaphragm to atmosphere.

Claims (10)

1. Measuring transducer for measuring pressure differences, having a relatively rigid pressure transducer converting the measured pressure into an electric signal, which transducer is part of a partition between two chambers filled with transmission liquid which are closed off from the process medium by separating diaphragms, and having an overload protection device for protecting the pressure transducer against unilateral overloading, characterised in that the three essential functional elements of the measuring transducer, the pressure transducer (1), the overload protection device (2) and the separating diaphragms (3,4) are accommodated each in its own housing block, the pressure transducer block (5), the overload protection block (6) and the separating diaphragm block (7), and these three housing blocks (5, 6, 7) are detachably connected with one another in the sequence stated.

2. Measuring transducer according to Claim 1, characterised in that the overload protection device (2) in a manner known perse comprises a bellows (30) made fast on two sides, the interior of the bellows (30) forming a chamber (43) which terminates to the exterior in a threaded opening (39) which is closed in pressure-tight manner with a stopper (40).

3. Measuring transducer according to Claims 1 and 2, characterised in that the bellows (30) is initially stressed in both directions by a spring (31), in that the bellows bottom (32) is firmly connected with a rod (33) which has a projection (34) which in common with a projection (35) in the housing block (36) forms the one support of the spring (31) and in that an internally threaded bush (37) screwed on to the rod (33) is provided which with an externally threaded bush screwed into the threaded opening (39) of the block (5) forms the other support for the spring (31).

4. Measuring transducer according to Claim 1, characterised in that the essential proportion of the hydraulic resistance of each of the two pressure transmission passages (16,17), which is generated by correspondingly narrow and long throughflow cross-sections for the damping of pressure pulses, lies within the separating diaphragm block (7).

5. Measuring transducer according to Claims 1 and 4, characterised in that two transmission passages (16, 17) extending straight through the separating diaphragm block (7) from the side wall (18) to the side wall (19) are present which are widened at the side wall (19) to form a threaded opening (20) which serves as filling opening for the introduction of the transmission liquid (21) and is closable with a ball (22) and screw (23), in that these two transmission passages (16, 17) in the separating diaphragm block (7) have a diameter of at least 3 mm. facilitating the introduction of the transmission liquid (21), and hydraulic resistance elements (26) are pushed into them for the provision of the requisite high hydraulic resistances.

6. Measuring transducer according to Claim 5, characterised in that the cylindrical hydraulic resistance elements (26) introduced into the transmission passages (16, 17) possess a larger diameter in the end lying between the ball (22) and the channel part (24) in the installed condition, which diameter due to press fit (27) or knurling (28) ensures firm seating in the transmission passage (16,17), and in thatthe hydraulic resistance element (26) has an internal threading (29) for easy withdrawal at this end.

7. Measuring transducer according to Claim 1, characterised in that due to omission of the overload protection block (6), the gaskets (46,47) and the connection element (9), the pressure transducer block (5) is detachably connected directly with the separating diaphragm block (7) by means of the connection elements (8,25).

8. Measuring transducer according to Claim 1, characterised in that due to omission of the measuring chamber lid (13), the separating diaphragm (4) on the minus side, the diaphragm carrier disc (11), the transmission liquid (21) and the hydraulic resistance element (26), the chamber (43) hitherto closed by the separating diaphragm (4) on the minus side is connected with the atmosphere.

9. Measuring transducer according to Claims 1,7 and 8, characterised in that the overload protection block (6), the gaskets (46, 47), the connection element (9) and, on the low pressure side, the measuring chamber lid (13), the separating diaphragm (4), the carrier disc (11), the transmission liquid (21) and the hydraulic resistance (25) are omitted and the chamber (43) hitherto closed by the separating diaphragm (4) is connected with atmosphere, so that with the same components a simplified pressure-measuring transducer without overload protection is realised.

10. Measuring transducer for measuring pressure differences substantially as described herein with reference to the accompanying drawings.