JPH0664678B2 - Analog input device - Google Patents

Description

TECHNICAL FIELD The present invention relates to an analog input device for converting an analog signal into a digital signal.

[Conventional technology]

FIG. 2 is a block diagram showing a conventional device of this type. In FIG. 2, (1), (2) and (6) are analog signal sources, (7) is a multiplexer, and (11) is an analog-digital conversion device. In this case, the analog-digital conversion device (11) includes an amplifier (21), an analog-digital converter (hereinafter abbreviated as A / D) (22), a data register (1
0). (12) is a communication conversion device,
The data temporarily stored in the data register (10) is read out and transmitted to the host controller or the like in a signal form suitable for transmission.

The analog signal sources (1), (2), (6) are, for example, various sensors, and when these sensors are thermocouples, the data required by the host controller etc. is the temperature measured by the thermocouples. However, 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, amplifier (21), A / D
The gain and offset of (22) fluctuate, and the amplifier (2
It is necessary to adjust the span with the volume control of 1).

Signal linearization, alarm check, conversion calculation to physical unit,
The sequence control function and the like are performed by the upper control unit.

[Problems to be solved by the invention]

Since the conventional device is configured as described above, the number of adjustment points increases, especially when the number of measurement points increases, and the calculation load of the host control unit is increased due to signal linearization and conversion calculation into physical units. Becomes large, and especially when the analog signal source is a thermocouple, it is necessary to perform linearization and span adjustment individually depending on the type of thermocouple, but there is a problem that this process is difficult.

The present invention has been made to solve the above problems. In the present invention, gain offset correction of an analog-digital conversion device can be automatically performed, and signal linearization and span adjustment can also be automatically performed. The purpose of the present invention is to provide an analog input device.

[Means for solving problems]

In the device of the present invention, a correction unit is provided in the latter stage of the A / D, and at least two types of reference voltage generating circuits are provided, and the reference voltage of the output of this reference voltage generating circuit is input to the analog-digital converter. The output of the analog-to-digital converter is used to correct gain and offset, and span correction and linearization are applied according to the type of analog signal source.

[Operation] The gain and offset of the analog-to-digital converter are automatically corrected, and the signal is automatically processed for span correction and linearization corresponding to the type of the 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.
The same reference numerals as those in the figure indicate the same or corresponding portions, (23) is a storage unit that stores the measurement range and the like for each measurement point, (24)
Is a correction unit, (25) is an interface, (26) is a control unit,
(27) and (28) are reference voltage generating circuits, (31) and
(32) and (36) are filters, respectively. However, a filter is not necessary for an analog signal source whose noise level is sufficiently low.

Next, the correction of the gain and the offset in the correction section (24) will be described. Analog signal source (1), (2),
The output voltages of (6) are v ₁ , v ₂ , and v ₆ , respectively, and the voltage values of the reference voltage generating circuits (27) and (28) are V _{2 7} and V, respectively.
And _{2 8,} respectively _{d 1} output in the case of entering these voltages to the amplifier (21) A / D (22 ), d 2, d 6, d 2 7, d 2
If it is ₈ , v ₁ = k ₁ d ₁ + a ₁ (1), v ₂ = k
_{2 d 2 + a 2 ... (} 2), v 6 = k 6 d 6 + a 6 ...
(3), V _{2 7} = k _{2 7} d _{2 7} + a _{2 7} (4), V _2
8 = k _{2 8} d _{2 8} + a _{2 8} (5) It is assumed that the amplifier (21) and the A / D (22) constitute an analog-digital conversion device, and inputs v ₁ , v ₂ , v ₆ ,
If the gain and offset of this analog-to-digital converter are constant in the range of V _{2 7} and V _{2 8} , k ₁ =
k ₂ = k ₆ = k _{2 7} = k _{2 8} = k ... (6), a ₁ = a ₂
= A ₆ = a _{2 7} = a _{2 8} = a ... (7), and k = (V _{2 7} −V _{2 8} ) / (d _{2 7} ) from equations (4) and (5).
-D _{2 8} ) ... (8), a = V _{2 8} -kd _{2 8} (9) To get

Since V _{2 7} and V _{2 8} are known, if d _{2 7} and d _{2 8} are measured, the values of d ₁ , d ₂ and d ₆ can be used to calculate equations (10), (11) and (12).
V ₁ , v ₂ and v ₆ can be calculated by

In addition, the storage unit (23) corresponds to each analog signal input,
If you store the lower limit value V _A and the upper limit value V _{B of the} voltage you want to measure, and the A / D (22) corresponding to V _A and V _B respectively, span correction will be performed. Can be performed by

It is also possible to add a linearization function to the correction section (24). For example, the conversion data table of thermocouple generated voltage vs. temperature is stored in the storage unit (23) in the form of ROM, and the data table in the storage unit (23) is stored according to the generated voltage data after correction of gain and offset. Can be searched to obtain a digital number representing the temperature.

Further, in the zero point compensation in the thermocouple, the voltage corresponding to the temperature of the terminal can be input to the amplifier (21) by switching the multiplexer and the correction can be performed by the same method as described above. For this purpose, a reference voltage generation circuit (27),
In addition to (28), another reference voltage generating circuit is provided. Therefore, when the analog signal input via the multiplexer (20) is the voltage generated by the thermocouple, the calculation process performed by the correction section (24) is as follows.

(B) When the output of A / D (22) is d, the true voltage v of the thermocouple corresponds to the equation (10). Calculated by, is calculated by (b) the temperature T corresponding to the generated voltage v is T = f (v) + T O ... (15). However, f (v) is obtained from the data table in the storage unit (23). T _O is the temperature of the reference junction used for zero compensation.

(C) Furthermore, perform span correction corresponding to equation (13). Is calculated. The control section (26) controls the operations of the A / D (22), the correction section (24) and the interface (25) by program control, for example.

〔The invention's effect〕

As described above, according to the present invention, an analog signal voltage is converted into a digital signal after amplification, gain and offset corrections are performed, linearization processing is performed if necessary, and if the analog signal voltage is a thermocouple generated voltage. After the cold spot compensation process is performed, the span correction is automatically performed if necessary, and the data is automatically output, so that the data suitable for the host controller can be obtained accurately. There is.

[Brief description 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), (2) and (6) are analog signal sources, (20) is a multiplexer, (21) is an amplifier,
(22) is an A / D, (23) is a storage section, (24) is a correction section,
(25) is an interface, (26) is a control unit, (26),
Each of (27) is a reference voltage generating circuit. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A multiplexer for selecting any one of a plurality of analog signals and outputs of at least two types of reference voltage generating circuits and connecting the selected one as an input of an analog-digital converter, said two types of reference voltage generating circuits. Two outputs of the analog-to-digital conversion device when each of them is connected as an input of the analog-to-digital conversion device, and any one analog signal selected from the plurality of analog signals is the analog-to-digital conversion device. From the output of the analog-to-digital converter when connected as the input of the analog-to-digital converter to the output of the analog-to-digital converter with respect to the arbitrary one analog signal assuming that the gain and offset of the analog-to-digital converter are kept constant. Apply gain correction and offset correction Analog input device comprising the Tadashibu.