JPH0216294Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a data measuring device equipped with a disconnection detection circuit for detecting disconnection of an input signal source.

The measuring device of the present invention has a means for insulating the mV level DC voltage signal represented by the thermoelectromotive force of the thermocouple in the input circuit. -It has been filed as No. 107511. Before explaining the present invention, the previously proposed insulation means will be explained with reference to FIG.

In FIG. 1, Ex is an input signal source, Dp is a diode circuit in which diodes D ₁ and D ₂ are connected in parallel and with opposite polarities, and the characteristics of the current I with respect to the voltage V are shown in FIG. 2. Similarly, Ds is a diode circuit in which diodes _D3 and _D4 are connected in parallel and with opposite polarities, and its V and I characteristics are similarly shown in FIG. T is a 1:1 small pulse transformer having a tertiary winding n ₃ , and an impulse current i ₀ is supplied to this tertiary winding n ₃ . C ₁ and C ₂ are capacitors,
The input circuit is composed of the capacitor C ₁ , the anti-parallel connected diode circuit Dp, and the primary winding n ₁ of the transformer T, and the output circuit is composed of the secondary winding n ₂ of the transformer T, the anti-parallel connected diode circuit Ds, and the capacitor C ₂ . is configured. If transformer T is an ideal transformer,
Voltages e 1 , e ₂ occurring in primary and secondary windings n _{1 ,} n ₂ and windings
For the currents i ₁ and i ₂ flowing through n ₁ and n ₂ , e ₁ = e ₂ , i ₁ + i ₂ =
If the relationship i ₀ is established and further considering the left-right symmetry seen from the transformer T, in the steady state, i ₁ =
i ₂ =i ₀ /2. If a current with amplitude ±I ₀ shown in Figure 3A is used as the impulse current i 0 supplied to the tertiary winding n ₃ , then i ₁ and _{i 2 have} amplitude ±I ₀ / as shown in Figure 3B.
2 pulse current.

In the V and I characteristics of diodes D ₁ , D ₂ , D ₃ and D ₄ shown in Fig. 2, the absolute values of the voltages between the terminals corresponding to I=±I ₀ /2 are Δ ₁ , Δ ₂ (D ₃ Δ ₁ ', Δ ₂ ') for D ₄ , the voltage e ₁ generated in the primary winding n ₁ of the transformer T becomes (Ex + Δ ₁ ) when the impulse current i ₀ is a positive pulse, i When ₀ is a negative pulse, (Ex−
Δ ₂ ). Similarly, the voltage e ₂ in winding n ₂ of the output circuit
As shown in Figure 3C, when i ₀ is a positive pulse, e ₂ =
E ₂ + Δ ₁ ′, and e ₂ = E ₂ − Δ ₂ ′ during negative pulse. Voltage
e ₂ is waveformed by capacitor C ₂ and becomes the output voltage E ₂ . This output voltage E ₂ is balanced at a value that satisfies e ₁ =e ₂ . In other words, the output voltage E ₂ is calculated using the following two equations: When i ₀ is a positive pulse...Ex+Δ ₁ = E ₂ +Δ ₁ ′ When i ₀ is a negative pulse...Ex− _{Δ 2 =} E 2 −Δ ₂ ′ It is derived as an additive average value.

E ₂ = Ex−Δ ₁ −Δ ₁ ′/2−Δ ₂ −Δ ₂ ′/2 (1) Therefore, if Δ ₁ = Δ ₁ ′, Δ ₂ = Δ ₂ ′, then E ₂
is equal to the input DC voltage Ex, and is a voltage that is electrically isolated from the input circuit. In addition, although the case where the tertiary winding _n3 is used for the transformer T is illustrated above, as shown in Fig. 4A, the impulse current source IP is the primary winding,
Secondary winding n ₂ of a transformer T with secondary windings n ₁ , n ₂
Alternatively, it may be connected between both ends of the parallel diode circuits Dp and Ds. In addition, diodes D ₁ , D ₂ , D ₃ ,
Instead of _D4 , a diode-connected transistor as shown in FIG. 4B may be used.

Such insulating circuits have a simple circuit configuration and can insulate low-level signals despite their small size, and are currently used in a variety of applications.

The present invention is a measuring device having such an insulating circuit in its input circuit, in which disconnection of the input signal source is automatically detected, and an embodiment thereof is shown in FIG. In Fig. 5, IS ₁ , IS ₂ , ... are the insulation circuits shown in Fig. 1, and Ex ₁ , Ex ₂ , ... are the insulation circuits shown in Fig. 1, respectively.
represents the input signal, and Rx ₁ , Rx ₂ , . . . represent the impedance of the input signal source, respectively. Thermocouples are often used as this input signal source. ρ ₁ and ρ ₂ are insulation resistances specific to the mounting components, respectively, and S ₁ , S ₂ ,...
...are respectively scanner switches, A is an amplifier,
AD is an analog-to-digital converter (hereinafter simply referred to as
(referred to as AD converter), CONT is arithmetic control circuit, DIS
is a display circuit, SB is a disconnection detection switch, IBS is a current source for disconnection detection, COP is a comparator, and ES is a reference voltage source. The insulation resistance ρ ₁ is connected in parallel to the capacitor C ₁ and the input signal source Ex ₁ is connected in parallel to the insulation resistance ρ ₁ . The insulation resistance ρ ₂ is connected in parallel with the capacitor C ₂ , and one of its connection points X
is connected to the input end of an amplifier A via a switch _S1 , and the output end of this amplifier is connected to a display circuit DIS via an AD converter and an arithmetic control circuit CONT. The input terminal of the amplifier A is further connected to a current source IBS via a switch SB, and is also connected to one input terminal of a comparator COP. The other input terminal of the comparator COP is connected to a common via the reference voltage source ES. comparator
The output end of COP is connected to the arithmetic/control circuit CONT. Insulated circuit IS ₂ , ... is also the above insulated circuit IS ₁
, and are connected to the input end of amplifier A via switches S ₂ , . . .

The operation for detecting a disconnection according to the present invention having such a configuration will be explained as follows. This disconnection detection is performed before or after the measurement of the input signals Ex ₁ , Ex ₂ . . . . Input signal Ex ₁ ,
To measure Ex ₂ ,..., scanner contacts S ₁ , S ₂ are turned on sequentially, and Ex ₁ , Ex ₂ ,... are connected to insulation circuits IS ₁ , IS ₂ ,... which operate based on the explanation in Fig. 1. Through
input signal to the AD converter, and this AD converter inputs the input signal
Ex ₁ , Ex ₂ , ... are sequentially converted into digital signals,
This is done by inputting to the arithmetic/control circuit CONT. Even when detecting a disconnection, the scanner contact S ₁ ,
Turn on S ₂ , ... sequentially. Now, Sukiyana contact point
When _S1 is on, disconnection detection switch SB is turned on.
When turned on at time t ₀ shown in the figure, the current source
The disconnection detection current IB obtained from IBS is
It flows through SB and _S1 to the output side capacitor _C2 in the isolation circuit _IS1 , thereby charging _C2 .
Almost simultaneously with this charging, the potential is transferred to the capacitor C ₁ of the input circuit. As a result, the voltage e _i of the capacitor C ₁ is shown as curve A in FIG. Next, in FIG. 6, switch SB is turned off at time _t1 , and the operation in this case will be discussed. Now, impedance Rx ₁ of input signal source Ex ₁
When is small, the charge in the input circuit capacitor C ₁ is discharged with the time constant of C ₁ and Rx ₁ , so its potential drops rapidly. The output voltage e ₀ of the isolation circuit IS also decreases almost simultaneously following the potential of the capacitor C ₁ . This situation is shown by curve B in FIG. On the other hand, when the impedance Rx ₁ of the signal source under test Ex ₁ is disconnected, the discharge time constant is C ₁ , ρ ₁ and C ₂ ,
ρ ₂ is typical, and it slowly attenuates as shown by curve C in Figure 6. Therefore, the comparator
If the value of the reference voltage Es used for COP is set as Ec, then
At a certain time (for example, time t ₃ ) after the switch SB is turned off, the comparison level Ec
In contrast, the curves B and C are clearly separated, and this difference is detected by the comparator COP.
In other words, if the input signal source Ex ₁ is disconnected, the comparator
Can be detected by COP. The disconnection of the input signal sources Ex ₂ , . . . is also performed sequentially in accordance with the above operation by turning on the switches S ₂ , . The output of the comparator COP is the calculation/control circuit
Input to CONT. With the signal obtained by the comparator COP, the arithmetic/control circuit CONT receives the measured signals Ex ₁ , Ex ₂ , which were input before (or after).
Determine whether the value of ... is significant or insignificant. display circuit
The DIS displays or prints the significant value of the signal to be measured obtained from the control circuit CONT as measurement data. In the above embodiments, multiple input points have been described, but the number of input points may be one, and the comparator COP may be connected to the output side of the amplifier A.

As explained above, according to the present invention, the primary and secondary
It has an insulation circuit consisting of a transformer with a secondary winding, two sets of diode circuits, and a pair of capacitors, and the disconnection detection current is supplied from the secondary circuit of this insulation circuit, so it is connected to the primary circuit. According to the present invention, it is possible to obtain a data measuring device that can automatically detect a disconnection of the signal source under test from the voltage of the secondary circuit.

[Brief explanation of the drawing]

Fig. 1 is a connection diagram of an isolation circuit used in the data measuring device of the present invention, Figs. 2 and 3 are diagrams for explaining the characteristics and operation of Fig. 1, and Fig. 4 is an illustration other than Fig. 1. FIG. 5 is a connection diagram showing an embodiment of the data measuring device of the present invention, and FIG. 6 is a diagram for explaining its operation. IS ₁ , IS ₂ , ... Isolation circuit, Ex ₁ , Ex ₂ , ... Signal source under test, AD ... Analog-to-digital converter, SB ... Switch for disconnection detection.

Claims (1)

[Claims for Utility Model Registration] A transformer having a primary winding and a secondary winding, two sets of diode circuits each having a pair of diodes connected in antiparallel, and a pair of capacitors; An input circuit is constructed by connecting one set of anti-parallel connected diode circuits in series and connecting one of the capacitors in parallel.
An output circuit is configured by connecting another set of anti-parallel connected diode circuits in series to the secondary winding and connecting another capacitor in parallel, and a An insulating circuit configured to give a pulse signal to one of the following windings, an analog-to-digital converter to which an output terminal of the insulating circuit is connected via a switch _S1 and an amplifier; A disconnection detection switch that is connected to the connection point between _S1 and the amplifier and turns on and off the disconnection detection current supplied to the output circuit of the isolated circuit via switch _S1 , and after turning off this disconnection detection switch. A data measuring device comprising a comparator for detecting the presence or absence of a disconnection in a signal source to be measured connected to an input circuit side of the insulating circuit based on the voltage e ₀ of the output circuit in the insulating circuit after a predetermined time has elapsed.