DE2557091C3 - Circuit arrangement for measuring and displaying the operating voltages of individual assemblies in radio and television receivers - Google Patents

Description

Threshold amplifiers are set so that at A first light-emitting element is exceeded when a lower limit value of the measuring voltage is exceeded, and when it is exceeded a second light-emitting element is also put into operation of an upper limit value of the measuring voltage, The reference voltages can be switched from measured value to measured value with.

Since, as suggested in the aforementioned DE-OS, the individual measured values via voltage divider to the ring counter can be supplied so that they can be normalized to a uniform value by Component tolerances of the measured value divided down by the ring counter fluctuate and possibly a measured value fiber or - pretend to be below the limit.

The invention is therefore based on the object to take these tolerances into account and to make the circuit independent of them. This task will solved by the measures characterized in the claims

This measure ensures that the two voltages are the first fixed reference voltage and the switched second reference voltage generated by the third operational amplifier, the tolerance window in which the measuring voltages may be in compliance with the required tolerances, be determined. The circuit was constructed in such a way that tolerances of the components used influence the measurement result as little as possible. To what extent Tolerances of components exert influence on the function of electronic circuits is in the Trade journal Funkschau 1975 issue 14, pages 85 to 88, as well as in volume 15, pages 45 to 46 dealt with in detail

The invention will be explained in more detail below with the aid of the drawing.

As already described in detail in DE-OS 25 10 504, the measuring voltages E \ to £ jv to be checked are given to this associated voltage divider 1, so that they are divided down to a standardized, close-tolerance, equal setpoint and to the inputs E \ to E'n a ring counter 2 can be switched. The ring counter 2 is switched on with the aid of a clock generator 3 via a switching stage 4, so that the divided measurement voltages present at the inputs E \ to E'n of the ring counter 2 appear in a serial output at the output Ao. The measuring point belonging to a measuring voltage is indicated at the outputs A \ to An with the help of the LEDs L \ to Ln The clock frequency of the generator 3 which advances the ring counter is selected so high that a flicker-free light display occurs The measured values appearing at the ring counter output A _{n appear in parallel} the inverting input of a first operational amplifier 5, and 6 on the non-inverting input of a second operational amplifier at "the non-inverting input of the first operational amplifier 5 is a fixed reference voltage Unt is applied while according to the invention connected to the inverting input of the second operational amplifier 6 is dependent on the Meßstellc reference voltage The second reference voltage is taken from the output of a third operational amplifier 7. The non-inverting input of this operational amplifier 7 is connected to the fixed reference voltage U _n /, which ζ, Ε is generated with the aid of a Zener diode 8. The operational amplifier 7 is an almost ideal non-inverting amplifier with feedback via the resistor 9 to the inverting input, which is, however, connected to a resistor 10 to a more or less fluctuating low potential of approx. T80 mV caused by the ring counter The output voltage of such an operational amplifier results in

While maintaining the feedback resistor 9, the output voltage Uj of the operational amplifier 7 can be changed by switching the resistor 10 is. Below are the values of this resistance for three tolerance ranges z. B. for 3%, 5% and 10%, the measuring voltages can be calculated.

The result is the formula for the resistance 10 according to M of the equation

_D _ U _ref - U _A. "

i \ in - ~ 77

lh - U _ref

Assuming that Rq is equal to 10 kohm, this results in the tolerance ranges ± 3% for Uj = 5.1 V + 3% = 5.253 V and Ua = 180 mV

_ 5.1-0.180
¹⁰ ~ 5.253-5.1

R ₁₀ = 321 kii.

10 kii.

The resistances 10 are calculated in a similar way for ± 5% to R 10 - 193 kohm and for ± 10% to λ10 - 96 kohm. These resistors with the different values matched to the various tolerance ranges are each connected to the outputs At to An of the ring counter 2 and, via these, place the inverting input of the operational amplifier 7 one after the other almost at ground potential. The voltage differences Uj-Urcf can still be faulty. Therefore, the input voltages fed to the inputs E ₁ to En are divided in such a way that they, including a residual voltage caused by the ring counter 2, correspond to the value of the reference voltage Unt. The measurement voltages occurring at the output M , together with the output voltage Ui , generate a partial voltage at the voltage divider formed by the resistors 11 and 12

Ui =

Uo + Ui

if RwRh is selected, ie the center voltage U \ shifts automatically according to a tolerance-related change in Ut, so that U \ always lies exactly between the voltages Unt and Uj, ie always in the middle of the tolerance field Voltage Lh by ± 10% ie 120% | can change before the error detection responds. This is the advantage over the usual formation of a tolerance window at the input of an operational amplifier using a voltage divider, in which the tolerances of the divider resistances are much greater when

use should not be made of two reference voltage sources.

The measurement voltage U \ is given to one input each of the operational amplifiers S and 6. The voltages U, rf and Lh reach the other inputs of the operational amplifiers, which work with a gain Vo- * oo. In the normal case, that is, if Unf <U \ <Lft and thus lies within the defined tolerance field, the output voltages of the operational amplifiers 5, 6 are equal to Ub- However, if the voltage difference t /, - £ Λ> 0, i.e. when the tolerance field is exceeded because U ₁ > Ui, the output of the operational amplifier 5 is switched to ground potential, and the light-emitting diode 13 connected to it lights up. If the voltage difference U _M f— U \> O ₁

ie when the tolerance limit is undershot, the light-emitting diode 14 lights up as a result of the decrease in the output voltage L / 6 of the operational amplifier 6. The cathodes of the light emitting diodes 13 and 14 are connected to the operating voltage Ub via a resistor IS. From this resistor 15, when one of the diodes 13, 14 lights up, a signal is picked up which, as a short pulse, actuates a shading stage 4 via the capacitor 17 to switch off the generator 3. A key switch 16 can start the counting cycle again. This ensures that the faulty measuring point is displayed until the measuring and testing process is consciously initiated again and is not automatically continued as soon as the fault happens to disappear again.

For this purpose I sheet drawings

Claims (2)

Claims; I ₁ circuit arrangement for measuring and displaying the operating voltages of individual assemblies in radio and television receivers using light-emitting diodes as display elements, which is housed in a cuboid housing and can be connected to the receiver circuit to be checked via a central plug-in device, ι ο where the to Checking operating voltages are connected to the inputs of a ring counter via these voltage dividers which bring them to a normalized value, the ring counter having outputs for luminous elements assigned to the measuring points as well as an output emitting the respective measured value and this output is connected to the inverting or non-inverting input of an operational amplifier is, to whose non-inverting or inverting input a reference voltage is connected, with a light-emitting diode being connected to the outputs of the operational amplifiers and the outputs of the operational amplifiers Above decoupling diodes are connected to a switching stage for shutting down the generator clocking the ring counter, a start button being arranged at the clock input of the ring counter for forced switching and the tolerance field for the voltages to be measured being changeable by switching the reference voltage, characterized in that the inverting input of a first operational amplifier (6) is connected to a fixed reference voltage Uni and ac the non-inverting input of a second operational amplifier (5) is connected to a second reference voltage (Uj) which can be switched from measuring point to measuring point as the output voltage of a third operational amplifier (7) with its non-inverting input to the first reference voltage source (8) with the reference voltage (U ₁ ^) , and its output is connected in a known manner via its fixed feedback resistor (9) to its inverting input, which is connected to the gefo Resistors (10) corresponding to the tolerance ranges are connected to the outputs (Ai to A ^ of the ring counter (2) connected to the light-emitting diodes (U to Ln) , the measuring voltage (Uo) and the output voltage (U ₁ ) of the third operational amplifier (7 ) are interconnected as a reference voltage via two resistors (11, 12) of equal size, whose connection point (U ₁ ) is connected to the inputs of the operational amplifiers (5, 6) 2. Circuit arrangement according to claim 1, characterized in that the light-emitting diodes (13, 14) are connected with their cathodes to the outputs of the operational amplifier (4,5), and that the anodes of the two light-emitting diodes (13, 14) via a common resistor (15) are connected to the operating voltage (Ub) , and that the anode-side connection of the resistor (15) is connected to a switching stage (4) which, if an error occurs, puts the generator (3) out of operation, and that the switching stage ( 4) is connected to a push button switch (16) with which the generator (3) can be put back into operation. The invention relates to a circuit arrangement for measuring and displaying operating voltages individual assemblies in radio and television receivers. The marking of faulty Measurement voltages, as well as the assemblies belonging to them, are carried out by means of light-emitting diodes, which are shown in a housing are arranged, which can be connected to the receiver via a central plug-in unit is In DEOS 2510504 such Proposed circuit, which has the advantage that by quickly querying the measuring points with the help of a Ring counter an apparently parallel display occurs when the clock frequency of the ring counter is selected so high that the light-emitting diodes shine without flickering to the eye. Two operational amplifiers are attached to the ring counter connected, to whose inverting or non-inverting inputs the output voltage of the Ring counter is placed, with reference voltages to the corresponding other inputs for formation a tolerance window are switched In this way, an indication is achieved which indicates whether a measured value is above and below the specified tolerance range. The circuit arrangement works in in such a way that the counter is stopped at the moment as soon as an output of the two operational amplifiers signals a faulty measuring voltage. A corresponding LED on the meter lights up and indicates the measuring point that is faulty, while all other light-emitting diodes go out, fet st by one forced restart of the counter, it runs until a subsequent faulty measuring point hits Further. This start can take place first of all by a switch that can be actuated manually or by it caused that the measured value falls back into the tolerance range by itself conditionally intermittent failure errors. However, this causes the error to be lost. so well there is in one. Radio or television receiver however, operating voltages that must be adhered to more precisely than others, that is, there are Measuring parts for which narrower and different tolerances must be observed. So it is not It makes sense if you wanted the same requirements for all voltages to be checked Provide accuracy, which would have to be based on the operating voltage with the tightest tolerance. So would accordingly, an operating voltage can be signaled as too high or too low, although the device is at this value would still be functional, because a slightly greater tolerance would be permissible. In "IBM Technical Disclosure Bulletin" Vol. 16, No. 9 from February 1974 on pages 2841 to 2842 is a display system for measuring voltage values described at. which two adjustable threshold amplifiers each control a display element. the