Measuring and testing – Dynamometers – Responsive to torque
Reexamination Certificate
1999-09-17
2001-12-04
Fuller, Benjamin R. (Department: 2856)
Measuring and testing
Dynamometers
Responsive to torque
Reexamination Certificate
active
06324921
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an inlet diaphragm construction between process side and measuring mechanism in a process measuring device.
BACKGROUND OF THE INVENTION
To measure various processes, process measuring devices are known in which a measuring sensor is placed in a process medium flow channel or the like, and the actual measuring means is placed outside this flow channel. In such a process measuring device, a sensing element is fixed to a lever-like transfer element for transmitting the force and/or movement exerted by the process medium on the sensing element by the torque principle to the measuring means outside the flow channel system. The measuring means is a force transducer for measuring the force dependent on the torque applied to the transfer element constituting the lever arm, the force being proportional to a variable to be measured, such as consistency of the process medium. The process medium flow channel is provided with a measurement coupling comprising an opening through which the lever arm is introduced. The process measuring device can thus be divided into a portion on the process side and a portion outside the process. A diaphragm is placed in connection with the opening in the measurement coupling to prevent the process medium from entering into the portion of the process measuring device that is located outside the process. However, because the torque effect of the force applied to the sensing element must be transmitted by the lever arm to the portion of the process measuring device outside the process, this diaphragm must be made as elastic as possible, so as not to cause distortions in the measuring result on one hand and not to make the measuring device too insensitive on the other hand. Furthermore, it is not desirable that the measuring result be affected by other factors than the variable to be measured.
The diaphragm is subjected to very high demands, because if entered in the portion of the process measuring device that is outside the process, the process medium may cause serious damage to the process measuring device and may even break the process measuring device. Thus, the process measuring device must be either repaired or replaced by a new one, which will in any case cause extra costs and may even require a stoppage of the process until the damaged process measuring device has been repaired or replaced by a new one.
Finnish patent 75424, to which corresponds e.g. U.S. Pat. No. 4,757,708, presents one inlet diaphragm construction. The diaphragm is fixed to the frame of the process measuring device on one hand and between the first and second rod parts of the lever arm on the other hand. Thus, the diaphragm covers the opening of the measurement coupling. The first rod part is intended to be placed on the process medium side in the flow channel and, correspondingly, the second rod part is intended to be placed outside the process medium flow channel. A sensing element if fixed to the first rod part. The first and second rod parts are attached to each other preferably with a threaded joint, wherein either of the rod parts is arranged to penetrate the opening formed in the diaphragm to make the threaded joint between the rod parts and to clamp the diaphragm between the first and second rod parts. In some phases of the process, such as in starts, so-called clods or other accumulations may pass in the flow channel and hit the sensing element so strongly that the first rod part bends. For this reason, existing measuring devices are equipped with a so-called mechanical fuse which is produced by making the rod part thinner. In spite of this mechanical fuse, this impact-like force effect may cause a slight opening of the joint between the first rod part and the diaphragm, allowing process medium to enter inside the process measuring device, and serious damage may consequently be caused.
SUMMARY OF THE INVENTION
It is an aim of the present invention to eliminate the above-mentioned drawbacks to a great extent and to achieve an improved diaphragm construction to prevent process medium from penetrating through diaphragm when the first rod part is bent. The present invention is characterized in that the diaphragm is fixed to the second rod part with a fixing element which comprises preferably a sleeve-like support portion and a preferably flange-like fixing portion. The invention is based on the idea that in conjunction with the second rod part there is a fixing portion to press the diaphragm against the second rod part and to transfer the impact force on the first rod part to the second rod part in such a way that the pressing force between the second rod part and the inlet diaphragm is not substantially changed.
With the present invention, significant advantages are achieved when compared to solutions of prior art. The inlet diaphragm construction according to the invention makes the diaphragm remain tightly against the second rod part also in such situations in which the sensing element is subjected to impacting forces. Thus, a crack cannot be formed in the joint between the second rod part and the diaphragm. Because the joint between the first rod part and the fixing element is primarily on the side of the process flow in the inlet diaphragm construction according to the invention, a slight opening of this joint will not yet cause the process medium to enter inside the process measuring device. By using the inlet diaphragm construction according to the invention it is possible to significantly reduce the maintenance and repair costs.
REFERENCES:
patent: 4062226 (1977-12-01), Hietala
patent: 4074097 (1978-02-01), Hutchinson et al.
patent: 4757708 (1988-07-01), Hietaranta
patent: 5157962 (1992-10-01), Fitzgerald et al.
patent: 5686660 (1997-11-01), Lundberg
patent: 5962795 (1999-10-01), Lambert
patent: 3204817 A1 (1983-08-01), None
Eerola Mika
Hietaranta Matti
Alston & Bird LLP
Davis Octavia
Fuller Benjamin R.
Metso Field Systems Oy
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