JPS6095329A - Analog input device - Google Patents

Abstract

PURPOSE:To detect a disconnection without exerting any influence on an input scan by generating an AC constant-current having a frequency stopped by a noise eliminating means when the disconnection is detected, applying it to a thermocouple, and comparing a generated voltage of an input part by the AC constant-current, with a reference voltage. CONSTITUTION:An output of a thermocouple 1 is inputted to a controlling circuit 15 through a noise eliminating signal conditioner 8 provided with a semiconductor protecting circuit 23, etc., and by a command of a disconnection detection controlling circuit 21 of the circuit 15, a current I of an AC constant-current source 22 is applied to the thermocouple 1, and an input part voltage (e) of the conditioner 8, which is generated at that time is inputted to the primary side of a pulse transformer 291 through a noise eliminating filter circuit 27, etc. Also, its secondary side voltage is inputted to a comparator 35 through an amplifier 31, etc., compared with a reference voltage VREF, and its disconnection detecting signal 100 is inputted to the circuit 15 and the circuit 21 is operated, by which the output of the thermocouple 1 is inputted to the conditioner 8.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an analog input device for inputting an analog signal generated by a thermocouple to a control circuit.

[Technical background of the invention]

FIG. 1 is a block diagram showing an example of a conventional analog input device of this type. The output signal of thermocouple 1 is connected to resistor 2,
After the noise is removed by the noise removing signal conditioner 8 which is composed of 3, 4.5 and a capacitor 6.7, 1 of the e-rus transformer 10 is removed via a point switch (using a semiconductor switch) 9. Applied to the next side. A signal induced on the secondary side of the pulse transformer 10 is input to an amplifier 13 via a point switch 11 and a group switch (consisting of semiconductor switches) 12.

The signal amplified by the amplifier 13 to a level capable of converting analog data into digital data is A.
The signal is converted into a digital signal by the /D converter 14 and input to the control circuit 15.

On the other hand, the control circuit 15 controls an insulated power supply 17 including a pulse transformer 16 to generate a constant voltage e1.

This constant voltage town is a resistor manufacturer 8. It is applied to the thermocouple 1 via the diode 19.20. This constant voltage e1 is divided through a voltage dividing circuit composed of a resistor 18 and a thermocouple 1, and a voltage e2 corresponding to the impedance of the thermocouple 1 is generated at the input of the signal conditioner 80 for noise removal. .

Next, the operation of the conventional analog input device configured as described above will be explained with reference to FIG. That is, when detecting a disconnection of the thermocouple 1, the control circuit engineer 5 turns on the insulated power supply 17 as shown in FIG.

Then, the insulated power supply 17 generates a voltage e1 as shown in FIG. 2, and this voltage e1 is applied to the thermocouple 1 via the resistor 18. At this time, the impedance of the thermocouple 1 and the voltage dividing valve e2 of the resistor 18 (see FIG. 2) are applied to the input of the sidinal converter 4 and 8. This voltage e2 increases when the thermocouple l is disconnected, as shown by the broken line in FIG.
o. In this state, when a scan request is issued to the thermocouple 10 input, a high voltage induced on the secondary side of the pulse transformer 1o is applied to the A/D converter 14tti.
Since this N converter 14 overflows as shown by the broken line in FIG. 2, disconnection of the thermocouple 1 is detected.

Please note that this analog input device is transformer isolated, so
Scansbee r has a high speed of several loμ8. Also, due to the relationship with the signal conditioner 8, the isolated power supply 17
Turning on and off is done in groups, not points.

[Problems with background technology]

When the thermocouple 1 is normal, the voltage e2 is as shown by the solid line in FIG. 2. At this time, the A/D converter 14 does not overflow, but the signal input to the control circuit 15 is The signal will be higher than that of signal 1. Therefore, in the analog input device of the type shown in Fig. 1, constant voltage e2 is applied to the input while detecting disconnection of thermocouple 1. The disadvantage is that it cannot be measured. Note that the portion indicated by the symbol T2 in FIG. 2 is the disconnection detection time of the thermocouple 1. In addition, since the analog human power device shown in FIG.
, JT,. ) had the disadvantage that it was not possible to detect a disconnection of thermocouple 1 or to perform a normal scan of thermocouple l.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to overcome the above drawbacks and provide an analog input device that can detect disconnection of a thermocouple without affecting signal input scanning from the thermocouple.

[Summary of the invention]

The present invention provides an analog input device that inputs an analog signal generated by a thermocouple through a noise removing means, in which an AC constant current having a frequency that is blocked by the noise removing means is generated when a disconnection of the thermocouple is detected, and the AC constant current is transmitted to the noise removing means. an AC constant current generating means applied to the thermocouple; and a voltage generated at the input section of the analog input device by the AC constant current, which is insulated from the input side through a filter that passes only this voltage;
The above object can be achieved by using an analog input circuit, which is equipped with a comparison means for comparing this with a reference voltage, and detects a break in the thermocouple by a signal outputted by the comparison means due to the high voltage generated when the thermocouple breaks. It is something to be achieved.

[Embodiments of the invention]

An embodiment of the analog input device of the present invention will be described below with reference to the drawings, with the same parts as those of the conventional example being given the same reference numerals. FIG. 3 is a block diagram showing an embodiment of the analog human power device of the present invention. The output signal of PA couple 1 is connected to resistor 2.3,
After the noise is removed by a noise removing signal conditioner 8 composed of a signal converter 4.5 and a capacitor 6.7, the signal is applied to the primary side of the pulse transformer 100 via a point switch 9. The signal induced on the secondary side of the pulse transformer 10 is input to the amplifier 13 via point switches 11 and 12. The signal, which has been amplified by the amplifier 13 to a level capable of converting the analog signal into a differential signal, is converted into a digital signal by the A/]) converter 14 and input to the control circuit 15.

A control circuit (xsKJd disconnection H detection control) Iff-ru section 21 is provided, and according to a command from this disconnection detection control section 21, an AC constant current source ρ is activated to generate a sine wave (hereinafter AC constant current) for detecting disconnection of the thermocouple 1. ) is generated. This ACC constant current is applied to the thermocouple 1. A semiconductor protection circuit 23 is inserted into the input section of the signal conditioner 80 to protect the input circuit elements from the high voltage generated when the thermocouple 1 is disconnected from the ACC constant current. The output side of the thermocouple 1 is connected to a noise removal filter circuit 27 composed of resistors 24, 25 and a capacitor 26, and the noise generated at both ends of the thermocouple 10 when the ACC constant current voltage flows through this circuit 27. That is, signal conditioner 8
'-pressure ek generated on the 0 input side, point switch 28
Input to the primary side of the pulse transformer 29 through.ノξ
The voltage induced on the secondary side of the transformer 290 is input to the amplifier 31 via the point switch 30, where the voltage amplified to a predetermined level is transferred to a signal clamp circuit consisting of a diode 32, a resistor 33, and a capacitor. The signal is input to the comparator 35 through. A reference voltage VRICF is applied to the comparator A, and this reference voltage V
A disconnection detection signal 100 of the thermocouple 1, which is a comparison result between REF and the input voltage, is input to the control circuit 15. The point switches 28 and 30 are turned on and off by a point switch r live circuit 36, and this drive circuit 36 is controlled by a disconnection detection control circuit 2.

The circuit of this embodiment has a configuration in which a disconnection detection circuit consisting of a noise removal filter circuit 27, a noise transformer 29, an amplifier 31, a comparator 35, etc. is added to a conventional analog input device. There is.

Next, the operation of this embodiment will be explained with reference to FIG. When the disconnection detection command from the disconnection detection controller 2J provided in the control circuit 15 is sent to the AC constant current source 22, this AC constant rd current source 22 generates a sine wave 500) Q for disconnection detection on the ACC constant current. degree) is applied to thermocouple 1. Then, a sinusoidal voltage e is generated at both ends of the thermocouple 1 due to the ACC constant current pressure corresponding to the impedance of the thermocouple 1. Since this voltage e is removed by the signal conditioner 8, only the voltage generated by the thermocouple 1 is applied to the point switch 9. Therefore, when the control circuit 15 requests a signal input scan of the thermocouple 1 in this state, the point switches 9 and 11
Then, the group switch 12 is turned on, and only the voltage generated in the thermocouple 1 is applied to the amplifier 13, and after being amplified to a predetermined level, it is converted into a digital signal by the A/D converter 14 and sent to the control circuit 1.5. is input.

On the other hand, the voltage e generated across the thermocouple 10 due to the ACC constant current is applied to the noise removal filter circuit 27 of the disconnection detection circuit.
After noise is removed there, the signal is applied to the tint switch 28. At this time, when the disconnection detection control unit 21 turns on the point switch 30 through the drive circuit 35, the voltage e is applied to the isolation transformer 2.
9'f: input to the amplifier 31 through. The output of the amplifier 31 is input to a comparator 35 via a flange circuit, where it is compared with the 411i quasi-voltage VREF. Comparator 35
outputs a disconnection detection signal 100 of the thermocouple 1 to the control circuit 15 at a logic level when the input voltage is higher than the reference voltage VREF. Note that under normal conditions when the thermocouple 1 is not disconnected, the voltage e is at a low level as shown by the solid line in FIG. 4, so the output of the comparator 35 remains at a low level.

Now, when the thermocouple 1 is disconnected, the impedance seen from the AC constant current source 22 is the line beadance between the thermocouple input circuit and the disconnection detection circuit, and the ACC constant current voltage flowing through the line beadance between the thermocouple input circuit and the disconnection detection circuit. As a result, a high voltage e indicated by the broken line in FIG. 4 is generated. At this time, turn on the point switch 30 of the disconnection detection circuit and apply the voltage e to the noggle transformer 2.
9 to the amplifier 31, amplified to a predetermined level, and compared with the reference voltage VREF applied to the comparator.
As shown in FIG. 4, since the output of the amplifier 31 is higher than the reference voltage VREF', the output of the comparator 35 becomes a signal as shown by the broken line in FIG. 4, and this is input to the control circuit 15. The control circuit 15 thereby detects that the thermocouple 1 is disconnected. Note that in the analog input device of this embodiment, the signal head scan of the thermocouple 1 is performed regardless of the VJjffM detection operation of the thermocouple 1.

According to this embodiment, when detecting a disconnection of the thermocouple 1, an AC constant current I is applied to the thermocouple 1 from the AC constant current source n, so that the voltage e generated by this AC constant current 1 and the voltage generated in the thermocouple 1 are different. The voltage generated by the thermocouple 1 is separated by the signal conditioner 8, and only the voltage generated by the thermocouple 1 is converted into a digital signal by the A/Di converter 14 and then inputted to the control circuit 15. This can be done without affecting the signal input scan from 1. Therefore, there is no time during which signal input to the thermocouple 1 is inhibited, and accurate temperature measurement can be performed at all times. In addition, when the thermocouple 1 is disconnected, the disconnection detection signal 1 from the comparator 35 is
00, it is possible to clearly determine whether or not the thermocouple 1 is disconnected. In addition, although the analog input device which inputs the signal from the thermocouple 1 was demonstrated in the said Example, it is not restricted to a thermocouple in any way.

[Effects of the Invention] As described above, according to the analog input device of the present invention,
When detecting a thermocouple disconnection, an AC current is applied to the thermocouple to generate an AC voltage across the thermocouple, and this AC voltage and the voltage generated by the thermocouple are separated by a filter so that the thermocouple is always connected. Since only the generated voltage is input, there is an effect that disconnection of the thermocouple can be detected without affecting the signal input scan from the thermocouple.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an example of a conventional analog input device, FIG. 2 is an operation time chart of the analog input device shown in FIG. 1, and FIG. 3 is an embodiment of the analog input device of the present invention. FIG. 4 is an operation time chart of the analog input device shown in FIG. 3. 1... Thermocouple 8... Signal conditioner for noise removal 9, 11.28.30... Point switch 10, 29... Pulse transformer 13.31...
・Amplification 514...A/D converter 15...Control circuit 21-...Disconnection detection control section 22...
・Constant current source 27...Noise removal filter circuit Figure 1 Figure 3 Figure 2 Electric power supply ez = '゛・, A/DC output buffer -m-・

Claims (1)

[Claims] In an analog input device that inputs an analog signal generated by a thermocouple through a noise removing means, when a disconnection of the thermocouple is detected, an AC constant current having a frequency that is blocked by the noise removing means is generated and applied to the thermocouple. AC constant current generating means for generating the AC constant current, and comparing means for taking in the voltage generated at the input section of the analog input device by the AC constant current through a filter that passes only this voltage, isolated from the input side, and comparing this with a reference voltage. An analog input device comprising: a disconnection of the thermocouple is detected by a signal outputted by the comparing means due to a high voltage generated when the thermocouple is disconnected.