JPS6256983B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to an insulation resistance meter.

The details of the insulation resistance meter are determined by JISC1302, and the insulation resistance value must be displayed on the scale of the indicator in a scale that approximates a logarithm.

Conventional logarithmic conversion circuits for insulation resistance meters include circuits that utilize the Zener characteristics of Zener diodes (for example, Utility Model Application No. 43,862/1986), and circuits based on approximate broken lines using diodes (eg, Utility Model Application No. 115,893/1989).
However, the former required a specially selected Zener diode, and the latter required a large number of parts.

The present invention utilizes the logarithmic relationship between forward voltage and current of a silicon diode to provide an insulation resistance meter equipped with a logarithmic conversion circuit having an extremely simple circuit configuration.

FIG. 1 is a diagram showing an example of the scale of an indicator that is intended to be realized by an insulation resistance meter according to the present invention.
In FIG. 1, 1 indicates the pointer of the indicator, and when no current flows through the indicator, it indicates the ∞ position. The section A in Figure 1, which is about 1/3 of the scale length, is a scale corresponding to the reciprocal of the resistance to be measured Rx.
The section B is a scale corresponding to the logarithm of the resistance to be measured Rx. FIG. 2 shows this in terms of the relationship between the current I flowing through the resistance to be measured Rx and the indicator current Im. Figure 2 shows that, for example, when the current I _l flowing through the resistance to be measured Rx is ImA, the pointer of the indicator swings to the full scale and indicates zero in Figure 1, and when the current I _l is less than 1 μA, the pointer of the indicator swings to the full scale. ∞ in Figure 1. Furthermore, the current I _l
In the range from about 1 to 10 μA, the indicator current Im is proportional to the current I _l , and when the current Il exceeds about 10 μA, the indicator current Im is proportional to the logarithm of the current I l.

FIG. 3 is a diagram showing an embodiment of the present invention. In FIG. 3, E is a DC high-voltage power supply, and D ₁ and D ₂ are diodes that are thermally balanced.

r _s and r ₁ are resistances, M is an indicator having an internal resistance r _n , and 1 and 2 are measurement terminals to which resistances to be measured are connected. A series circuit consisting of a high-voltage power supply E, a diode _D1 , and a resistor _r1 is connected between the measurement terminals 1 and 2. A series circuit of an indicator M, a resistor r _s and a diode D ₂ is connected to both ends of the diode D ₁ .

The operation of the apparatus shown in FIG. 3 configured and connected in this manner will be described below.

A resistance to be measured Rx is connected between measurement terminals 1 and 2. Let Il be the current flowing from the high-voltage power supply E to the resistor to be measured Rx, and Im be the current flowing to the indicator M.

Generally, the forward voltage across the diode is V
It is known that the relationship of equation (1) holds if _d is the current flowing in the forward direction and I _d is the current flowing in the forward direction.

I _d = Is・{exp(q・V _d /k・T)−1} (1) Is: Reverse saturation current q: Electron charge k: Boltzmann constant T: Absolute temperature (1) Equation (2) It can be rewritten as a formula.

V _d =k・T/q{ln(Is+I _d )−lnIs} (2) On the other hand, let the voltage across the diode D ₁ in Figure 3 be V _D
1. If the voltage across diode _D2 is V _D2 (3)
The formula holds true.

V _D1 =V _D2 +( _rs + r _n )·Im (3) The following equation (4) is established from equations (2) and (3).

Im=1/ _rs + _rn・k・T/q{ln(Is+Il−Im)
-ln(Im +Is)} (4) When the indicator current Im is large, that is, in the case of section B in Figure 1, the large current flowing through the diodes D ₁ and D ₂ is due to the effect of the resistors r _s and r _n depending on
The relationship Is≪Im≪Il holds true. Therefore, equation (4) becomes (5)
It can be rewritten as a formula.

k・T/( _rs + r _n )・q・lnIl = Im+k・T/( _rs + r _n )・q・lnIm (5) In Figure 4, the right side of equation (5) is replaced with Y, and the This shows the relationship. In Figure 4, the straight line indicates Y=Im, and the curve indicates Y=k・T/( _rs + r _n )・
q・lnIm is shown, and the dotted line is Y=Im+k・T/( _rs + r _n )・q・
Showing lnIm. Figure 4 shows the indicator current Im as described above.
is a large area and is drawn as Is≪Im≪Il, so the graph of section B in Fig. 4 (corresponding to section B in Fig. 1) correctly shows the magnitude corresponding to indicator current Im. It represents. On the other hand, since the section A in FIG. 4 is a region where the indicator current Im is small, unlike the above conditions, it does not correctly represent the magnitude corresponding to the indicator current Im. From the above, in the section B of Figure 4, straight lines are dominant, so the following equation (6) holds true.

Im≒k・T/( _rs + r _n )・q・LnIl (6) When the indicator current Im is large, that is, in the section B in Fig. 1, from equation (6), the indicator current Im is the resistance to be measured Rx It is proportional to the logarithm of the current Il flowing through.

Next, when the indicator current Im is small, (r _s + r
_n )・Im will be a small value. Therefore, equation (7) can be derived from equation (4).

I _s +I _l -I _n /I _n +I _s ≈1 (7) From equation (7), the following equation holds true.

Im≒I _l /2 (8) In other words, when the indicator current Im is small (the first
In the section A in the figure), the indicator current Im is proportional to the current I _l flowing through the resistance to be measured Rx from equation (8).

From the above, in the section A in Fig. 1, the resistance to be measured Rx is very large and can be set as I _l = E/Rx. Therefore, in the section A in Fig. 1, the resistance to be measured is The scale corresponds to the reciprocal of the measured resistance Rx.

Im≈E/2·Rx (9) In the section (b) of FIG. 1, the resistance to be measured Rx is relatively small, so the resistance r ₁ cannot be ignored and Il=E/Rx+r ₁ . Therefore, the section B in FIG. 1 has the relationship expressed by equation (10).

Im≒k・T/( _rs + _rn )・q{lnE−ln(Rx+ _r1 )
}(10) In other words, the section B in Figure 1 is the resistance to be measured Rx
The scale is approximately proportional to the logarithm of .

In FIG. 3, in order to explain the present invention in an easy-to-understand manner, the diodes D ₁ and D ₂ have been explained as having a configuration each consisting of one diode.
D ₁ and D ₂ may be constructed by combining multiple diodes in parallel or in series. In this case, the sensitivity of the indicator can be changed depending on the combination of diodes, and the scale of the indicator can be changed to suit the purpose. It has the effect that it can. For example, if diode D ₂ is constructed of n diodes connected in parallel as shown in FIG. 5, a constant term will be included in equation (4), and the constant on the right side of equation (8) will change.

Note that it is desirable that the diodes used in the present invention are thermally balanced, and good results can be obtained by using diodes formed on the same substrate (wafer).

In general, the indicator M has a linearity error, but the first
If the scale of the indicator shown in the figure is manufactured by printing, then in order to correct the linearity error of the indicator M, the logarithmic curve of equation (10) must be changed. Conventionally, correction was performed using a plurality of variable resistors each incorporated in a broken line circuit, but in the present invention, the resistance r
By setting _s to be a variable resistance, the indicator current Im can be varied as is clear from equation (10), and thereby the linearity error of the indicator can be easily corrected.

As described above, according to the present invention, logarithmic conversion of an insulation resistance meter can be performed with a very simple configuration consisting of two diodes, a resistor, and an indicator, and the effect is extremely large.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an example of the scale of an indicator of an insulation resistance meter, Fig. 2 is a diagram showing the relationship between the current I _l flowing through the resistance to be measured Rx and the indicator current Im, and Fig. 3 is a diagram showing the present invention. FIG. 4 is a diagram showing the function of equation (5), and FIG. 5 is a diagram showing another embodiment of the present invention. E...High voltage power supply, _D1 , _D2 ...Diode, _r1 ,
r _s ...Resistance, M...Indicator.

Claims (1)

[Claims] 1. First and second diodes that are mutually thermally balanced and are composed of one or more diodes, the first diode and the first diode being connected in parallel to the first diode. An insulation resistance meter comprising a series circuit including the second diode, a resistor, and an indicator.