JPS61199199A - Analog input unit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an analog input device that converts minute analog signals into digital signals.

[Conventional technology]

Figure 2 is a block diagram showing a conventional device of this type. The analog-to-digital conversion device (11) is composed of an amplifier (21), an analog-to-digital converter (hereinafter abbreviated as Φ) (22), and a data register (1). (12) is a communication conversion device. , the data temporarily stored in the data register (1) is read out, converted into a signal form suitable for transmission, and transmitted to the upper control unit, etc.

The analog signal sources +1), +2), and +61 are, for example, various sensors, and if this sensor is a thermocouple, the data required by the upper control unit etc. is the temperature measured by the thermocouple. There is no linear relationship between this temperature and the voltage output from the thermocouple, and this relationship differs depending on the type of thermocouple. Furthermore.

The gain and offset of the amplifier (21) and A/D (22) fluctuate, and it is necessary to adjust the span and the like with the volume of the amplifier (21).

Signal linearization, alarm checking, conversion operations to physical units,
Sequence functions and the like are performed in the upper control section.

[Problem that the invention seeks to solve]

Since conventional devices are configured as described above, especially when the number of measurement points increases, the number of adjustment points increases, and the calculation load on the upper control unit due to signal linearization, conversion calculations to physical units, etc. If the analog signal source is a thermocouple, it is necessary to perform linearization and span adjustment individually depending on the type of thermocouple, but this process is difficult.

This invention was made to solve the above-mentioned problems, and the invention automatically makes it possible to correct the gain offset of an analog-to-digital converter, and also automatically makes it possible to linearize the signal and adjust the span. The purpose is to provide an analog input device that is

[Means for solving problems]

In the device of the present invention, a correction section is provided at the subsequent stage of k, and at least two types of reference voltage generation circuits are provided, and when the reference voltage output from the reference voltage generation circuit is input to the analog-to-digital conversion device, the analog-to-digital converter is We decided to perform gain and offset correction using the output of the converter, and also perform span correction, linearization, etc. in accordance with the type of analog signal source.

[Effect]

The gain and offset of the analog-to-digital converter are automatically corrected, and a signal is output that has been automatically subjected to processes such as span correction and linearization corresponding to the type of analog signal source.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention, in which the same reference numerals as in FIG. 2 indicate the same or corresponding parts, and (23
) is a storage unit that stores the measurement range for each measurement point, (24) is a correction unit, (25) is an interface,
(26) is a control unit, (27) and (28) are reference voltage generation circuits, respectively, (31), (32), and (3
6) are each a filter. However, a filter is not necessary for analog signal sources whose noise level is sufficiently low.

Next, the correction of gain and offset in the correction section (24) will be explained. Analog signal source [11, +21.

The output voltage of (6) is Vt # V2 e 'I
s, the reference voltage generation circuit (71), (28)
Let the voltage values of each be v27°V2B, and the output of the A/D (22) when these voltages are input to the amplifier (21) are d□e dg t d, #d27. dz
s, then vl = 1 d l + al-(1
), 72 = 2(12+ 82 +*+ (2),
Vs = kadg +a6 ・= (3), 27d27 to v27 ``'27'''' (4), 28 to v28=
It can be expressed as d28+a28...-(5). Assume that the amplifier (21) and A/D (22) constitute an analog-to-digital converter, and the inputs v1 # v2 p
v6 p V27 m If the gain and offset of this analog-to-digital converter are constant in the range of V2B, k□= k2= k, , = k27= 2g
=k"・161, al"'2='6 ="27 ='2
g ='...(7), and from equation (4), C5) = (v27-v28)/(d27-d28)...(8
),' =V28- kd2g ``'' (9) is obtained, so d2- d28 v2= -Akebono τ;-(V27- V2B ) +V2g
−(11), since V and V are known, d
, d t-If measured, d, , d2. d6
From the values of Equations (10) and (11).

V□# 72 t Vs can be calculated by (12).

In addition, the storage unit (23) stores the lower limit value of the measured voltage (7 people) and the upper limit value (vB1) corresponding to each analog signal input.
This can be done by calculating (13).

It is also possible to add a linearization function to the correction section (24). For example, a conversion data table of thermocouple generated voltage versus temperature is stored in the storage unit (23) in the form of ROM,
A digital number representing the temperature can be obtained by searching the data table in the storage section (23) using the generated voltage data after the gain and offset have been corrected.

Further, cold spot compensation in a thermocouple can be performed by inputting the specific voltage corresponding to the temperature of the terminal to the amplifier (21) by switching the multiplexer, and performing correction by a method similar to the method described above. For this purpose, a reference voltage generation circuit (27)
, (28), one more reference voltage generation circuit is provided. Therefore, when the analog signal input via the multiplexer (20) is the voltage generated by a thermocouple, the computation processing performed by the correction section (24) is as follows.

b) When the output of the A/D (22) is d, the true generated voltage V of the thermocouple corresponds to equation (10), and -d2g' = d2. -, 128 ('i'27- v28)"
(b) The temperature T corresponding to the generated voltage M is calculated as T = f (v) + To = (15). However, f (v) is obtained from the data table in the storage unit (23). T is the temperature of the reference junction used as cold spot compensation.

(c) Furthermore, the span correction corresponding to equation (13) is T-TA D=TB-TA(D,-DA)・DA...(16
). The control section (A), for example, is programmed to control the A/D (η), the correction section (24)',
Controls the operation of the interface (25).

〔Effect of the invention〕

As described above, according to the present invention, a fine analog signal voltage is amplified and converted into a digital signal, gain and offset correction is performed, linearization processing is performed if necessary, and the analog signal voltage is a thermocouple generated voltage. If necessary, cold spot compensation processing is performed and, if necessary, span correction processing is automatically performed to output data, so data in a format suitable for use by the host control unit can be obtained accurately. There is an effect.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is a block diagram showing a conventional device. In the figure, (1), (21, and (61) are respectively analog signal sources, (20) is a multiplexer, and (21
) is the amplification unit, (22) is the Φ, (23) is the storage unit, (
24) is the correction section, (25) is the interface% (2
6) is a control section; (26) and (27) are reference voltage generation circuits, respectively. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (4)

[Claims] (1) A multiplexer that selects any one of a plurality of analog signals and the outputs of at least two types of reference voltage generation circuits and connects it as an input to an analog-to-digital converter, and the output of the reference voltage generation circuit is The output of the analog-to-digital converter when connected as an input to the analog-to-digital converter and the output of the analog-to-digital converter when any one analog signal selected from the plurality of analog signals is connected as the input to the analog-to-digital converter. An analog input device comprising a correction section that corrects the output of the analog-to-digital converter for any one of the analog signals from the output of the analog-to-digital converter and outputs the result. (2) The correction unit calculates the above-mentioned value for the output of the two types of reference voltage generation circuits and the analog-to-digital converter for the arbitrary one analog signal, assuming that the gain and offset of the analog-to-digital converter are kept constant for the output of the two types of reference voltage generation circuits and for the arbitrary one analog signal. 2. The analog input device according to claim 1, wherein gain correction and offset correction are applied to the output of the analog-to-digital conversion device. (3) The analog input device according to claim 1, wherein the correction section includes means for performing span correction according to the type of analog signal connected as an input to the analog-to-digital conversion device. (4) The analog input device according to claim 1, wherein the correction section includes means for performing linearization processing according to the type of analog signal connected as an input to the analog-to-digital conversion device.