JPS6366606A - Calibration system for current output circuit - Google Patents

Abstract

PURPOSE:To calculate the input value of a calibration system for current output circuit from the correction data as well as the ideal digital input value corresponding to the current output value at the time of outputting a current by calculating the correction data from the relation from the value obtained by converting digitally the output current signal and the digital input value and storing this calculated correction data. CONSTITUTION:A precise load resistance 3 for calibration is connected between current output terminals 1 and 2 of a current output circuit. The input terminals of an A/D converter 11 are connected to both ends of the resistance 3. At the same time, a digital signal of 0% is supplied from a man-machine interface and the A/D conversion value A0' between terminals of the resistance 3 is obtained by a processor unit. Then the A/D value A100' is obtained with input of a digital signal of 100%. The processor unit obtains the prescribed correction data A and B from the digital conversion values A0'-A0 and A100'-A100 and stores them in a memory. Here A0 and A100 show the ideal conversion values.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a current output circuit used as a component of a process control system, for example, and relates to a calibration method thereof.

[Conventional technology]

In a process control system, for example, a program adjustment needle can be used to control digital input values within a predetermined range, e.g. 4 to 29 meters.
A current output circuit that converts the signal into a current signal of A and outputs the signal is often used. In that case, the relationship between the digital input value For example, in the same figure, Io=Ia
Ideally, it would be sufficient to set x = x B, but in reality, it is necessary to set x = xa'.

Therefore, it is necessary to perform calibration in advance and obtain data for performing the correction.

Conventionally, such calibration is generally performed by the following method. That is, first, as shown in FIG. 5, a precise load resistor 3 for calibration is connected between the target current output terminals 1 and 2, so that the terminal voltage can be monitored with a voltmeter 4.

Next, the zero adjustment is performed to match the zero point, and the span adjustment is performed to match the maximum variable value.Specific methods include a hardware method using a volume, and a software method.

For the former, when inputting digital signal values of 0% and 100%, adjust each volume for zero adjustment and span adjustment while watching the voltmeter 4 so that the ideal voltage value can be obtained.
It is adjusted using a screwdriver, etc.

The latter can be set to 0% and 100% by pressing a key to increase or decrease the input value while looking at the voltmeter 4 (digital voltmeter).
Find the digital signal value that will give you the ideal voltage. The difference between that value and the ideal digital value is stored as correction data, and when the current is actually output, the value calculated from the ideal digital value and correction data is used as the digital input value. do.

[Problems to be Solved by the Invention] As described above, according to the conventional calibration methods, both the hardware method and the software method use a dedicated measuring device (voltmeter) and a volume control using a screwdriver. The tedious task of searching for the optimal value by gradually changing the υ input value by pressing a gate type or up/down key is required.

[Means for solving problems]

The present invention includes means for digitally converting an output current signal, provides a plurality of digital input values in advance, and outputs the output current signal in each case.
Correction data is calculated and stored from the relationship between the digitally converted value of the c-flow value and the digital input value.

At the time of the recirculation output, a digital signal obtained from the ideal digital input value corresponding to the output value and the correction data is given as the digital input value.

[Effect]

Correction data can be calculated by simply providing an arbitrary digital input value.

〔Example〕

As shown in FIG. 1, the current output terminal 1 of the current output circuit.
A precision load resistor 3 (resistance value R; 250Ω in this embodiment) for calibration is connected between the terminals 2 and 2. The steps up to this point are the same as in the case of the conventional calibration method. Analog-digital (
AD) Connect to the converter 110 input terminal. A like this
The D converter 11 is normally attached to, for example, a program controller, and it is sufficient to use it, and there is no need to prepare it specially.

In the following, an AD conversion value Ao' of the voltage between the terminals of the resistor 3 is determined in the processor unit by applying a digital signal of 0% to the example Everman Machine Inter7 Ace. Next, similarly calculate the AD conversion value Aloo' when 100% digital signal is given.O Ideal AD when 0% and 100% digital signal is input
Letting the converted values be Ao and A100, respectively, the processor unit will be Ao'Ao and A100'-A
From loo, corrected data A and B are obtained as follows and stored in the memory.

Next, an example will be described in which the digital input value is actually corrected using the values of Ao'-Ao and A100'-A100. It is assumed that the relationship between the digital input value and the current output value is as shown in FIG. In the figure, I indicates the ideal relationship, ■ indicates the actual relationship, Xα is the ideal 4% digital input value,
Xα' represents the actual 4% digital input value, and ΔXα represents the difference between the two. Further, 8°b indicates each full span of the digital input value and the current output value. Note that here, to simplify the calculation, a e b e c = Ao' - Ao
jd=Axoo'-Aloo.

It is assumed that the resolutions of Δxo and ΔX 100 are the same as that of the human conversion value (in this case, a = b).

Figure 2. It is expressed as follows.

Xα - Gradient Xα' = (Xα - Δxo) + (ΔXO - ΔX100)X
(-) Su100-Aya=Axα-B ・・・・・・・・・
(3) In other words, the correction data is obtained as follows.

The above description has been about the case where correction data is obtained by a manual method in which the next command is given to the machine interface, but it may also be done automatically by running a program for calibration. An example is shown in FIG. For example, when the calibration mode is set by a predetermined key operation, the processor unit
% digital value is output (step 101). And A
After a waiting time of, for example, several IQms until the output of the D converter 11 stabilizes (step 102), the AD converted value of the voltage value that resonates with the product of the output current value Is and the load resistance value B is read, and the value is is stored in a predetermined area of memory (step 103). In addition, in the case of manual operation, the AD conversion process will be performed after waiting for a predetermined operation.

Similarly, AD conversion values for 100% digital values are stored (steps 104 to 106). Thereafter, as described above, the correction data A and B are calculated from equations (4) and (5) (step 107), and the values are stored in a predetermined area of the memory (step 108).

If the correction data is obtained in advance in this way, when the east-side current is output, the corrected digital input value Xα corresponding to the output value and the above-mentioned correction data A and B can be used as shown in FIG. By finding the input value Xα' and applying the deviation to the current output circuit, it is possible to perform the cylindrical tone and the span tone.

〔Effect of the invention〕

As explained above, according to the present invention, the present invention includes a means for digitally converting an output current signal, and provides a plurality of digital input values in advance, and the relationship between the digitally converted value outputted in each case and the original digital input value is provided. Zero adjustment and span adjustment can be performed very easily by calculating the correction data from , and using the digital value obtained from the ideal digital input value and the above correction data as the input value during actual current output. .

Unlike the conventional example, there is no need to manually vary the input value while looking at the output of the measuring device to find the optimum value, and the measuring device itself is also no longer necessary.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing an example of the present invention, Fig. 2 is a diagram showing an example of input/output characteristics of a current output circuit, Fig. 3 is a flowchart showing a procedure for calculating correction data, and Fig. 4 is a diagram showing an example of input/output characteristics of a current output circuit. FIG. 5 is a circuit diagram showing a conventional example, and is a diagram showing an example of input/output characteristics of a current output path. 1.2...φ・Current output terminal, 3...Load resistance, 1
1...AD converter.

Claims (1)

[Claims] A current output circuit that converts a digital input value into a current signal within a predetermined range and outputs the current signal has a means for digitally converting the output current signal, and the digital conversion value of the output current value when a plurality of digital input values is given in advance. Calculate and store correction data from the relationship with the above digital input value, and when outputting current, give the digital value calculated from the ideal digital input value corresponding to the output value and the above correction data as the digital input value. A calibration method for a current output circuit characterized by the following.