JP2017067642A - Field apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To establish a noise filter circuit favorable for intrinsically safe instrumentation and realize an intrinsically safe apparatus that permits intrinsically safe instrumentation without worrying about the apparatus's own capacity for intrinsically safe explosion-proofing.SOLUTION: In a field apparatus in which a terminal board and internal circuitry are connected via a filter circuit, the filter circuit is configured as a filter module.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a field device, and more particularly to an improvement of a filter circuit module used for reducing the influence of external noise in a field device such as a differential pressure / pressure transmitter.

  For example, in a differential pressure / pressure transmitter, as shown in FIG. 9, there is a filter circuit that bypasses noise in order to reduce the influence of external noise on the inside of the equipment as a countermeasure against on-site noise generated in the usage environment of the equipment. Is provided.

  FIG. 9 is a block diagram showing an example of a conventional transmitter. The terminal block 1 is connected to the internal circuit 3 via the filter circuit 2.

  In FIG. 9, the filter circuit 2 includes coils La and Lb connected in series to the signal lines L1 and L2, respectively, and connected in series between the signal lines L1 and L2, and a connection middle point is connected to a common potential point. It consists of a single capacitance Ca, Cb.

  Since field devices such as differential pressure / pressure transmitters are used in hazardous areas with explosive atmospheres such as gas plants, mechanisms of explosion-proof structures such as intrinsically safe explosion-proof are incorporated.

  In intrinsically safe explosion-proof, energy storage components such as inductors and capacitors are limited in usable capacity, and these must be taken into account when designing the circuit of the entire device.

  In particular, filter circuits provided as countermeasures against external noise are often provided near terminal blocks that are accessed externally, and therefore the capacitance of inductors and capacitors used there is greatly related to the length of the wiring cable.

  FIG. 10 is a conceptual diagram of intrinsic safety instrumentation in a transmitter. In FIG. 10, the transmitter 4 is arranged in a dangerous area, the safety holder 5 is arranged in a non-hazardous area, and the power terminal of the transmitter 4 and the safety holder 5 are connected via a wiring cable 6. Yes.

  In designing intrinsic safety instrumentation as shown in FIG. 10, for example, the following relational expression is used in selecting energy storage components such as inductors and capacitors used in the circuit.

Ci + Cw ≦ Co
Li + Lw ≦ Lo
Ci: Transmitter internal capacitance Li: Transmitter internal inductance Cw: Wiring capacitance Lw: Wiring inductance Co: Safety cage allowable capacitance Lo: Safety cage allowable inductance

  Here, if the internal capacitance Ci of the transmitter can be set to a negligible value, all the allowable capacitance Co of the safety cage can be applied to the wiring capacitance Cw. Therefore, the parameter of the internal capacitance Ci of the safety device is considered. Wiring can be done without it.

That is,
Ci ≒ negligible value = 0
Then,
Cw ≦ Co
become.

  Patent Document 1 describes a technology that can satisfy high explosion-proof specifications and achieve high-performance wireless communication without using a pressure vessel.

JP 2012-115121 A

  By the way, in many cases, the length of the wiring cable in the intrinsically safe instrumentation is determined by the internal capacitance of the transmitter.

  As for the capacitance used in the filter circuit of the transmitter, a feedthrough capacitor or the like is often placed between the housing and the ground (between the ground), and the capacitance Ci in the transmitter is determined in consideration of them.

  In the intrinsically safe design, there is a method of setting the intrinsic capacitance to a value that can be practically ignored by configuring an intrinsically safe circuit using a blocking diode, but this method is not necessarily sufficient with respect to the capacitance between the casings.

  In addition, when the replacement of the intrinsically safe device occurs in the user's existing instrumentation, since the parameters of the intrinsically safe device differ depending on the product, it is essential to review the wiring length.

  The present invention solves these problems. The purpose of the present invention is to establish a noise filter circuit suitable for intrinsically safe instrumentation, and to perform intrinsically safe instrumentation without being aware of the capacitance of the device itself. The realization of safety equipment.

In order to achieve such a problem, the invention according to claim 1 of the present invention is:
In field devices where the terminal block and internal circuit are connected via a filter circuit,
The filter circuit is configured as a filter circuit module.

The invention according to claim 2 is the field device according to claim 1,
The filter circuit includes a current limiting resistor connected in series with a capacitor.

The invention according to claim 3 is the field device according to claim 1 or 2,
The parameters of the capacitor and the current limiting resistor constituting the filter circuit satisfy the conditions of the intrinsically safe explosion-proof structure standard.

According to a fourth aspect of the present invention, in the field device according to any one of the first to third aspects,
The filter circuit is provided so that a plurality of systems can be selected.

The invention according to claim 5 is the field device according to any one of claims 1 to 4,
The capacitor constituting the filter circuit is a blocking capacitor or a filter capacitor.

  According to such a configuration, a noise filter circuit suitable for intrinsically safe instrumentation can be established, and a field device capable of intrinsically safe instrumentation can be realized without being aware of the capacitance of the instrument itself in terms of intrinsically safe explosion protection.

It is a block diagram showing a specific example of a field device based on the present invention. FIG. 2 is a configuration explanatory diagram illustrating a specific example of a field device configured based on the configuration block diagram of FIG. 1. FIG. 3 is an assembly configuration diagram of FIG. 2. 4 is another block diagram of the configuration of the filter circuit module 2. FIG. 2 is a conceptual diagram of a filter circuit including a resistor R and a capacitor C. FIG. It is a block diagram of a filter circuit module including inductors and capacitors. It is a block diagram which shows the other Example of this invention. It is another block diagram of the filter circuit module 2 used in the present invention. It is a block diagram showing an example of a conventional transmitter. It is a conceptual diagram of the intrinsically safe instrumentation in a transmitter.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a configuration block diagram showing a specific example of a field device based on the present invention, and the same reference numerals are given to portions common to FIG. In FIG. 1, a filter circuit module selection unit 4 is connected between the terminal block 1 and the internal circuit 3, and a filter circuit module group 5 including a plurality of modularized filter circuits 2 is connected to the filter circuit module selection unit 4. It is connected.

  The filter circuit module selection unit 4 selects a desired filter circuit module that matches the purpose required by the transmitter internal circuit 3 from the filter circuit module group 5, or a plurality of filter circuits are provided in the same module. If the desired filter circuit is selected, a desired filter circuit module or a desired filter circuit is connected between the terminal block 1 and the internal circuit 3.

  FIG. 2 is a configuration explanatory view showing a specific example of a field device configured based on the configuration block diagram of FIG. 1, and the same reference numerals are given to portions common to FIG. In FIG. 2, the terminal block 1 is provided in the vicinity of the right side surface of the field device 10, and the modularized filter circuit module 2 keeps a predetermined distance from the terminal block 1 along the left direction of the terminal block 1. It is fixed with screws.

  The internal circuit 3 is distributed and mounted on two circuit boards 3a and 3b provided so as to be orthogonal to each other. One circuit board 3a is screwed and fixed to the filter circuit module 2 along the left direction of the filter circuit module 2 so as to maintain a predetermined distance, and the other circuit board 3b is connected to the filter circuit module 2 and one circuit. It arrange | positions so that it may orthogonally cross with the board 3a, and is screwed and fixed.

  FIG. 3 is an assembly configuration diagram of FIG. 2, and parts common to FIG. In FIG. 3, the filter circuit module 2 is screwed and fixed to a predetermined position inside the field device 10 via a fixing screw 4.

  A plurality of (three in this embodiment) connection pins 11 that are electrically connected to predetermined terminals of a terminal block (not shown) are provided at the attachment position of the filter circuit module 2 of the field device 10.

  On the other hand, the filter circuit module 2 includes a plurality of (three in this embodiment) so as to be electrically connected to the connection pins 11 when the filter circuit module 2 is mounted at a predetermined mounting position of the field device 10. Module pins 21 are provided.

  FIG. 4 is a block diagram showing another configuration of the filter circuit module 2. The filter circuit module 2 of FIG. 4 is provided with a module pin 21 and a plurality of filter circuits (not shown), and a changeover switch 22 for selecting a desired filter circuit from the plurality of filter circuits. ing.

  In this case, for example, the capacitor constituting the filter circuit is switched according to the switching of the selector switch 22.

  FIG. 5 is a conceptual diagram of a filter circuit composed of a resistor R and a capacitor C. (A) shows an example in which the current limiting resistor R and the capacitor C are connected in series, and (B) shows the current limiting resistor R connected in series to one signal line L1 and the capacitor C connected between the signal lines L1 and L2. An example is shown. In any of these circuit configurations, the current limiting resistor R and the capacitor C are regarded as one aggregate, and the resistance value of the current limiting resistor R is set so that the capacitance of the capacitor C is negligible on the intrinsically safe explosion-proof structure. decide.

The value of the capacitance of the capacitor C that can be ignored is either 1) or 2) below.
1) Less than 1% with respect to the value of the ignition curve of the capacitance C of the intrinsically safe explosion-proof structure standard and the specified table 2) Less than 1% with respect to the allowable capacitance Co of the safety cage

As a method of determining the resistance value of the current limiting resistor R, the following is used.
1) Application of mitigation rate table by resistance against capacitance C of intrinsically safe explosion-proof structural standards (IEC 60079-11 etc.) 2) Test measurement results by spark ignition test

  In addition to a general capacitance, a capacitance such as a filter capacitance or a blocking capacitance that is considered not to cause a failure in the intrinsically safe structure may be used.

  FIG. 6 is a configuration block diagram of a filter circuit module composed of an inductor and a capacitor, and the same reference numerals are given to portions common to FIG.

  In FIG. 6, an inductor La is connected in series to the signal line L1, and an inductor Lb is connected in series to the signal line L2. A series circuit of a capacitor Ca, a current limiting resistor Ra, a current limiting resistor Rb, and a capacitor Cb is connected between the signal lines L1 and L2, and two diodes D1 and D2 are also connected in parallel. The connection point between the current limiting resistor Ra and the current limiting resistor Rb is connected to a common potential point.

  Here, blocking capacitors are used as the capacitors Ca and Cb. By using the blocking capacitance, it is considered that the capacitors Ca and Cb are not short-circuited to each other (between ground). By connecting the current limiting resistors Ra and Rb in series with these capacitors Ca and Cb, the intrinsically safe structure is negligible, and the current limiting resistors Ra and Rb are not powered by the blocking capacitance. There is also a merit that power can be saved.

  In addition, regarding the two diodes D1 and D2 connected between the signal lines L1 and L2 as shunts, the stored energy of the inductors La and Lb can be regarded as a negligible value with respect to the safety cage side in the intrinsic safety design. I am doing so.

  In addition, it is not necessary to consider the space between the housings (between grounds) due to the blocking capacitance.

  As a result, the filter circuit module configured as shown in FIG. 6 can be considered to have negligible values for the inductors La and Lb and the capacitors Ca and Cb. The capacitor constituting the filter circuit is not limited to the blocking capacitor, and may be a filter capacitor.

  The essence that intrinsic safety instrumentation can be performed without being aware of the capacity of the device itself by preparing a plurality of filter circuit modules 2 as shown in FIG. 6 and using them appropriately as shown in FIG. Safety equipment can be realized.

  FIG. 7 is a block diagram showing the configuration of another embodiment of the present invention. In FIG. 7, the terminal block 1 functions as an input unit for an external temperature sensor, and a wiring cable for connecting an external temperature sensor such as a thermocouple or a resistance temperature detector is connected to the terminal block 1.

  Thus, the present invention can also be applied to a filter circuit module of an external temperature sensor input unit such as a temperature transmitter.

  FIG. 8 is also a block diagram showing another configuration of the filter circuit module 2 used in the present invention. A voltage limiting diode is connected to the filter circuit module.

  In FIG. 8A, two diodes D3 and D4 are connected in parallel with the capacitor C in a series circuit of a current limiting resistor R and a capacitor C connected between the signal lines L1 and L2. As a result, the voltage of the capacitor C is limited by the diodes D3 and D4.

  In FIG. 8B, a current limiting resistor R is connected in series to one signal line L1. A capacitor C is connected between the signal lines L1 and L2 at one end of the current limiting resistor R, and two diodes D5 are connected in parallel with the capacitor C between the signal lines L1 and L2 at the other end of the current limiting resistor R. D6 is connected. As a result, the voltage for the combination of the capacitor C and the current limiting resistor R is limited by the diodes D5 and D6.

  With the configuration shown in FIG. 8, the voltage applied to the capacitor C constituting the filter circuit module is limited by the diodes D3 to D6 connected in parallel. The capacity can be increased.

  As described above, according to the present invention, a noise filter circuit suitable for intrinsically safe instrumentation can be established, and field devices capable of intrinsically safe instrumentation without being aware of the capacitance of the instrument itself in terms of intrinsically safe explosion prevention. Can be realized.

DESCRIPTION OF SYMBOLS 1 Terminal block 11 Connection pin 2 Filter circuit module 21 Module pin 22 Changeover switch 3 Transmitter internal circuit 4 Filter circuit module selection part 5 Filter circuit module group

Claims (5)

In field devices where the terminal block and internal circuit are connected via a filter circuit,
The field device, wherein the filter circuit is configured as a filter circuit module.   The field device according to claim 1, wherein the filter circuit includes a current limiting resistor connected in series with a capacitor.   The field device according to claim 1 or 2, wherein the parameters of the capacitor and the current limiting resistor constituting the filter circuit satisfy an intrinsic safety explosion-proof structure standard.   The field device according to claim 1, wherein the filter circuit is provided so that a plurality of systems can be selected.   5. The field device according to claim 1, wherein the capacitor constituting the filter circuit is a blocking capacitor or a filter capacitor.

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