FR2522155A1 - Lead battery electromotive force measuring appts. - uses variable gain voltage amplifier to compare battery voltage and adjustable stabilised reference voltage and peak detecting circuit - Google Patents

Abstract

This device measures the peak values of a non-periodical phenomenon which has a low recurrence, where a variable decreases in a discontinuous fashion. It can be used, for example to measure the electromotive force of a lead battery. A variable gain voltage amplifier receives on its positive input a voltage which represents the voltage to be measured and on its negative input an adjustable stabilised voltage. Its output signal is applied to the positive input of a voltage comparator which receives, on its negative input, the voltage from an impedance converter. The input of the converter is connected to a peak detecting circuit consisting of a very low leakage capacitor and a low leakage diode.

Description

1 2522155

  The present invention relates to a device for

  to measure the peak values of a nonrecurring phenomenon with recurring

  is an improvement to the device according to the request of

  Main Patent No. 79 25 598 of 15 79.

  In this one has been described a realization applied more

  particular to the indication of the state of discharge of a lead-acid battery It is known that the measurement of the electromotive force, function

  linear density of the electrolyte, is representative of this state.

  In the industrial truck, the electromotive force of the battery decreases in approximately 7 to 8 hours from 2.15 volts at full load to 1.95 volts per cell, corresponding to a reduction of 80% in the rated capacity of this battery In no case

  it must not be unloaded beyond, under penalty of premature wear.

  Hence the need for accurate, stable and reliable measurement.

  In practice, the direct measurement by a voltmeter is excluded, because if theoretically the decay of the voltage integrated in time is linear, practically it varies discontinuously in successive stages These are separated by time intervals

  of random duration, during which the voltage can

  However, the duration of each of these intervals is small compared to the duration

  It is therefore necessary to integrate the credited values

  tension, while seeking a decrease in

  this of the latter with respect to time according to a determined slope corresponds to

  to the use made of the battery during its discharge.

  In the main patent, the case of a handling truck using a battery whose decay of the electromotive force as a function of time is on average a few micro volts / second. In order to achieve a low cost realization, we eliminated

  all systems using digital techniques, and other

  sophisticated analogizations, and according to the invention, it has been preferred an analog measurement using a peak storage capacitor

  voltage, the discharge of which is reduced to a value as low as

  thanks to the use of operational amplifiers with high

  In the intervals where the hoist system is used, the electromotive force drops to a

  very low value, as mentioned above The capacitor of

  moire then discharges a small quantity, but higher than the normal one.

  maliciously permissible to follow the previously fixed slope of discharge

2522 1 55

  The battery on 7 or 8 hours This discharge of the order of a hundred microvolts / second is inevitable in the framework of a good realization

  market and causes an error on the reading of about 2%.

  At the end of this period, the capacitor is recharged

  the rise of the electromotive force and the error practically canceled.

  The cycle begins again until complete discharge which has the effect of actuating any warning device or possibly blocking the lifting system This embodiment is therefore perfectly suitable

  as part of a normal use of the industrial truck.

  However, it may be desirable to use such a device in the case where the average actual discharge slope of the battery relative to

  at the time is weaker or stronger, which leads to control the decreasing

  the output voltage either by increasing or decreasing it.

  It is the device allowing this improvement which makes

  subject of this application for addition.

  The invention will be better understood from the description which

  will follow with reference to the accompanying drawings given by way of non-limiting example.

  tif and in which: Figure 1 is the representative diagram of the phenomenon to be measured. Figure 2 is a diagram of the electronic circuit according to the invention.

  In the diagram of Figure 1, a number of

  a decrease slope (right dl) which is the normal discharge slope of a battery for 7 to 8 hours (A Usl low) As mentioned above, it is used to memorize the upper peaks of the battery voltage, a capacitor 14 (FIG. 2) which discharges during the voltage dips, along an exponential branch d 2 of slope P This is at time zero, charged to Us mfx and then discharged according to the formula: Log Usmax n / a CR is the UsmaxK constant s 1 = CR time and dt the time interval needed to reach a voltage equal to Us max 8 Usl in the absence of battery voltage peak 4 Usl corresponds to a full-scale measurement range on the output indicator If we increase to Usl so that Us 2 = kf Usl, L is increased by a factor k'dt C

k ', CR to constant CR.

  The output indicator is then stopped, it is set to

  end up in the previous conditions.

  So, the indicator needle will take a longer time

  only in the first case to reach the bottom of the scale.

3 2522155

  It is as if the time constant of the circuit had been increased by the same factor k 'This fact is one of the characteristics

main features of the invention.

  In the main patent application, 6 Us is directly used at the battery terminals, which is, as we saw above, 0.2 v /

  According to the invention, this variation will therefore be increased or decreased.

  while retaining the same CR time constant, that it is

  difficult to increase without expensive complication.

  The scheme of realization is indicated by way of example in

  FIG. 2 The battery voltage to be measured is applied across a set of

  2 resistors 1 and 2, Ri being adjustable to reduce the voltage

  in A around the zener tension 19.

  This voltage is compared in the amplifier 8 to another fixed voltage taken from the slider of the potentiometer 4 in series with the resistor 5.

  all at the terminals of the zener diode 19 fed by the resistor 3.

  The gain of the comparison made by the amplifier 8 between VA and VB is set by the resistor 7, mounted in counter-reaction on this amplifier U is taken at the terminals of the Zener diode 10 The set R 9 and Z 10 ensures

  the limitation of U to the value Vz 10, in the case where the voltage VA reaches

  should be prohibitively expensive, especially when the battery is

recharge.

  The part of the diagram comprising the amplifiers 11 and 18 is identical to that of the main patent The amplifier compares the output voltage Us to U The output thereof is connected to a diode

  12, low leakage, and resistance 13 through which the neck passes.

  charging capacitor 14, when the voltage U

  is greater than Us (upper levels) When U <Us (lower levels)

  The capacitor 14 is discharged. The voltage V, stored, is applied

  at the positive input of the amplifier 18, mounted in gain of 1

  resistors 15, 16 and 17 provide an increase in the input impedance.

We have: Us' V and V the U max.

  The voltage variation at the output of the amplifier 18, e Us, as a function of time depends on 2 factors: one is non-adjustable; this is the discharge of the capacitor

  14 in the input stage of the amplifier 18.

  the other is adjustable; this is the amplitude of the variation of the battery voltage over time (a U) Referring to FIG. 1, we see that the average theoretical slope of C Us 1 discharges a lead-acid battery (anglec) is equal az s, in the case

  of its normal use in a handling truck.

4 2522155

e U = U max U min C 0.2 v / element.

  The amplification of A U and therefore of A Us at the output is equivalent to increasing

  ficially the theoretical slope of discharge of this battery (angle ce) and vice versa It thus becomes possible to adapt this slope to the discharge slope P of the capacitor 14 In other words, during the time o the

  battery voltage during an intensive discharge reaches a lower

  the decay slope of V may be identical to the

  theoretical slope, which obviously minimizes errors (A re-

  that by reciprocity we can also say that it is the

  aunt of C 14 discharge time that has been increased) The variation of

  The output (A Us) is operated by a measuring device.

  The measuring range is effected by adjusting the resistance 21.

  This mode of indication is given as a non-limiting example. Light-emitting diodes (LEDs) or lamps can also be used.

  or a liquid crystal display, or electroluminescent, of

  to make a display with successive equidistant marks

  and arranged rectilinearly or circularly without changing anything

of the invention (FIG. 3)

2 5 2 2 1 5 5

Claims (4)

R E V E N D I C A T IO N S   1 Device for measuring the peak values of a low recurrence non-periodic phenomenon, in which a variable decreases discontinuously as a function of time in successive steps separated by   intervals of random duration, during which said variable de-   grows insignificantly, the duration of each of the intervals being small compared to the total duration of the decay,   Characterized in that it comprises a voltage comparator   sion whose amplification factor is adjustable receiving on its input   positive the voltage representative of the voltage to be measured, and on its   a stabilized adjustable voltage, the result of the comparison   its being applied to the positive input of a second voltage comparator   which receives on its negative input the voltage coming from an appropriate circuit   impedance meter having a high input impedance and a low output impedance at the input of which is connected a charging and discharging circuit having a low reverse current diode and a load resistor, in series with the output of the voltage comparator, followed by a discharge circuit formed of a capacitor and a resistor connected between the high terminal of the capacitor and a divider bridge formed by two resistors connected in series on the output of the amplifier mounted in   gain of one, realizing impedance matching.   2 Device according to claim 1, characterized in that the phenomenon to be measured is the force   electromotive battery lead-acid battery.   3 Device according to claim 1 and 2, characterized in that the assembly comprises between the output of the first comparator and the positive input of the second limiting circuit   voltage consisting of a resistor and a zener diode.   4 Device according to claim 3,   Characterized by the fact that it includes in the output an indi-   meter constituted by a voltmeter, comprising means for adjusting the stroke of the needle.   Device according to claim 4, characterized in that the output indicator can be   made by bars or superimposed distinctive points, arranged   vertically or vertically, the amplitude of the variable being physically   either by 1 position of a mark on the scale, or by a number of marks.