JP2924166B2 - Signal transmitter - Google Patents

Description

The present invention relates to a two-wire signal transmitter for transmitting a current signal related to a physical quantity to a load via two wires, and more particularly to a two-wire signal transmitter such as a span or zero point. The present invention relates to a two-wire signal transmitter improved so that when a parameter affecting an output current signal is changed, the changed value can be quickly followed.

<Prior Art> A conventional two-wire signal transmitter usually converts a physical quantity into an electric signal and transmits a current signal corresponding to the physical quantity to a load via two signal lines. Since there is a pulsation, the signal is transmitted as a current signal with little fluctuation by performing predetermined damping.

<Problems to be Solved by the Invention> Therefore, in such a conventional two-wire signal transmitter, the current signal fluctuates when, for example, the span or the zero point is changed. The current signal is gradually changed according to a preset time constant.

As shown in FIG. 4, when the span of the current signal value output before the setting change is changed at time t1 as shown in FIG. 4, the current signal value is output according to the preset time constant toward the current signal value after the setting change. The problem is that it changes gradually and lacks responsiveness.

Also, when the damping time constant is set to a large value, it takes time for the current signal value flowing to the load to have an effect even if the zero point is changed. There is also a problem that this is the case.

<Means for Solving the Problems> In order to solve the above problems, the present invention converts a physical quantity to be measured by a sensor into an electric signal, processes the signal by a signal operation means including a microprocessor, and transmits the signal to a transmission line. A setting means for outputting a setting change signal of a parameter affecting a current signal to a microprocessor in a signal transmitter for transmitting a current signal to a load side through a microprocessor, and when a predetermined setting change is executed by the setting change signal Prediction operation means for performing an operation by a microprocessor so that a current signal becomes a predicted current value, and a damping operation is performed using the predicted current value to make a time constant immediately after a parameter change substantially zero. And a damping calculating means.

<Operation> The setting means outputs a setting change signal of a parameter affecting the current signal to the microprocessor, and the predictive calculating means causes the current signal to be changed by the setting change when the predetermined setting change is executed by the setting change signal. The calculation is performed by the microprocessor so that the predicted current value is obtained.

Next, the damping calculation means executes a damping calculation using the predicted current value to make the time constant immediately after the parameter change substantially zero.

In this way, when the parameter setting is changed, the time constant is temporarily set to zero and the current signal is automatically executed so as to quickly obtain the changed current signal, thereby improving the response speed.

<Example> Hereinafter, an example of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing the configuration of one embodiment of the present invention, and FIG. 2 is a flowchart showing the procedure of the operation executed in FIG.

Reference numeral 10 denotes a two-wire signal transmitter that converts physical quantities such as process variables into electric signals and transmits the electric signals.
Power is supplied via 12. The electric signal is transmitted as a current signal through the transmission lines l ₁ and l ₂ , and a voltage change occurring at both ends of the load 12 is detected to know a process variable.

The current signal is converted into a unified current of 4 to 20 mA from a two-wire signal transmitter 10 set to a range corresponding to the pressure in the pipe, transmitted to the receiving instrument 13 on the load side, and output to the monitor, for example. Digital display of digits.

In this case, for example, when it is desired to change or monitor the pressure range, it is convenient if it can be operated from outside the two-wire signal transmitter 10.

Therefore, the handheld terminal 14 is connected to the transmission lines l ₁ and l ₂
The two-wire signal transmitter 10 is provided with a dedicated data communication function with the hand-held terminal 14 by using the connection lines l ₁ ′ and l ₂ ′ as necessary. Digital data such as parameter change is transmitted to the expression signal transmitter 10.

Among them, the two-wire signal transmitter 10 is configured as follows.

The SNR is a sensor that detects pressure / differential pressure and converts it into an electric signal. The converted analog signal is converted into a digital signal by an analog / digital converter A / D and stored in a memory MEM via a microprocessor μP. Is stored in the random access memory part of The microprocessor μP uses the stored digital signal to execute a predetermined operation such as linearization in accordance with an operation procedure written in, for example, a read-only memory portion of the memory MEM, and via the digital / analog converter D / A. Output to the output circuit OPC.

On the other hand, a predetermined calculation result by the microprocessor μP is digitally displayed in a necessary number of digits on a built-in monitor LCD.

The output circuit OPC digital / analog converter D / A transmission line to convert a voltage signal converted into an analog signal into a unified current signal I _L of 4~20mA at l _1, received via the l ₂ instrument 13 To be transmitted. Also, OPC of the output circuit produces the power supply of the internal circuit of the 2-wire signal transmitter 10 with a portion of the current signal I _L.

In this case, for example, the monitor LCD is a value corresponding to the current signal I _L is digitally displayed.

SW is a setting switch, and the handheld terminal 14
It is used when the range is changed or the zero point is set by the two-wire signal transmitter itself even without it.

The IFC is an interface for data communication with the handheld terminal 14, is connected between the transmission lines l ₁ and l ₂ and the microprocessor μP, and converts digital signals from the transmission lines l ₁ and l ₂ into parallel data. It has the function of transmitting the data from the microprocessor μP to the transmission lines l ₁ and l ₂ as serial signals.

Next, the handheld terminal 14 is configured as follows.

SER is a setting device operated by an operator, and has a built-in monitor. Model requests two-wire signal transmitter 10, it is possible to change the display resolution, change of the range, change in the zero point, the abnormality detection, or display various settings or requests, such as the value of the current signal I _L.

μP ′ is a microprocessor, for example, a setting device SE
Data is input from R, and a digital signal is transmitted to the two-wire signal transmitter 10 via the interface IFC 'in accordance with the processing procedure stored in the memory MEM'. Further, the microprocessor μP ′ takes in the response data from the two-wire signal transmitter 10 into the memory MEM ′ via the interface IFC ′, decodes the data according to the processing procedure stored in the memory MEM ′, and sets the Display on the monitor.

Next, a processing procedure of damping when changing the span by the microprocessor of the two-wire signal transmitter 10, which is a main part of the present embodiment, will be described with reference to FIG.

The detector SNR detects a physical quantity, for example, a differential pressure or a pressure (step), and converts this into an electric signal.

The analog / digital converter A / D converts the electric signal into digital data. The data is taken in at a predetermined timing by the microprocessor μP and stored in a predetermined area of the memory MEM.

The microprocessor μP corresponds to the physical quantity detected by the detector SNR according to the arithmetic program stored in the memory MEM using the stored data, that is, executes linearization when necessary, and so on.
A predetermined measurement value X (n) is calculated and stored in a predetermined area of the memory MEM (step).

Thereafter, the output value Y corresponding to the absolute value of the previous current signal I _L that has already been stored in the memory MEM in step
Read (n-1).

The step is a step of calculating a damping output value.

In the step, the previous output value Y (n-n-
The damping output value Y of this time is softened using 1).
Stores (n) is in a predetermined area of the memory MEM operation, and outputs a current signal I _L through the output circuit OPC digital / analog converter D / A.

Assuming that Ts is a signal sampling period and Td is a time constant, the dumping output value Y (n) is Y (n) = Y (n-1) + [Ts / (Ts + Td)] X [X (n) -Y (N-1)] (1) where m is a damping value (m = 1, 2,...) To simplify the calculation, and [Ts / (Ts + Td)] = 1 / If it is assumed to be 2 ^m , the damping output value Y (n) is as follows: Y (n) = Y (n-1) + (1/2 ^m ) X [X (n) -Y (n-1)] 2) is calculated by

More steps to S indicates the operation process for outputting a normal current signal I _L that do not accompanied configuration changes.

However, when changing the setting, the transmission line can be set directly from the setting switch SW or from the handheld terminal 14.
Digital signals for instructing setting change are output to the microprocessor μP via l ₁ and l ₂ and the interface C (step).

The step reads the previous damping output value Y (n-1) stored in a predetermined area of the memory MEM.

Thereafter, the process proceeds to step varying change amount ΔY showing a change corresponding to the current signal I _L that is scheduled after the setting change, for example, the zero point on this read-out damping output value Y (n-1) At this time, an addition operation for adding a value corresponding thereto is performed to calculate a damping output value Y '(n-1) after the setting is changed. That is, Y ′ (n−1) = Y (n−1) + ΔY (3) is calculated.

In the step, the damping output value Y '(n-1) calculated in this way is stored in a predetermined area of the memory MEM as the previous damping output value Y (n-1).

After that, the process proceeds to the step and executes the damping calculation represented by the equation (2).

Therefore, since the use of the prediction value predicted change amount ΔY showing a change corresponding to the current signal I _L shown in (3) as the previous damping output value Y (n-1) is just after the setting change, to the setting change As a result, a fast response with a time constant of substantially zero is obtained.

The above situation is shown in FIG. As shown in the figure, immediately after the time point t2 of the setting change, it can be seen that the new value is immediately followed. This is clear from the comparison between the conventional response shown in FIG. 4 and the response according to the present embodiment shown in FIG.

<Effects of the Invention> As described above in detail with the embodiments, according to the present invention, the damping output value is not affected by the previous damping output value with respect to the setting change, but only by the current measurement value. Because it is configured to be determined, it responds quickly to the setting change such as the change of the zero point or the change of the span only immediately after the change, and after reaching the new value, damping is applied with the conventional time constant, The changed value can be reflected on the current signal faster.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of one embodiment of the present invention, FIG. 2 is a flowchart showing an operation procedure of the embodiment shown in FIG. 1, and FIG. 3 is a response diagram of the embodiment shown in FIG. FIG. 4 is a characteristic diagram showing a response to a setting change of a conventional two-wire signal transmitter. 10 two-wire signal transmitter, 11 DC power supply, 12 load, 13 receiving instrument, 14 handheld terminal,
SNR: Detector, μP: Microprocessor, IFC ...
Interface, SW: Setting switch, SER: Setting device.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-57-73495 (JP, A) JP-A-63-168571 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G08C 19/02

Claims (1)

(57) [Claims] 1. A signal transmitter for converting a physical quantity to be measured by a sensor into an electric signal, processing the electric signal by a signal operation means including a microprocessor, and transmitting the processed signal as a current signal to a load via a transmission line. Setting means for outputting a setting change signal of a parameter affecting a current signal to the microprocessor, such that the current signal becomes a predicted current value when a predetermined setting change is executed by the setting change signal. A prediction operation means for performing an operation by the microprocessor; and a damping operation means for executing a damping operation using the predicted current value to make a time constant immediately after the parameter change substantially zero. Signal transmitter.