CS219481B1 - Connection for digital tolerance metering of the resistance - Google Patents

Description

BACKGROUND OF THE INVENTION The present invention relates to circuitry for digital tolerance measurement of resistors with automatic equalization of active bridge circuitry.

So far, various measurement methods have been used for tolerance resistance measurements. A very common method is bridging measurement of resistors, where either a resistor bridge is connected manually or automatically, in which one measured resistance is connected. Although this method is very accurate, it is fast enough in automatic alignment, but its disadvantage is that the resistance value is expressed in absolute terms and the tolerance must be calculated or solved inside the instrument by a built-in counting logic. The additional calculation is inconvenient and can easily be a source of errors. Instruments with built-in counting logic are unnecessarily complex and expensive for most tolerance measurements. Therefore, for tolerance measurements, input and output resistance checks, analog tolerance ohmmeters with a pointer meter are used.

In these devices, the low speed and accuracy of measurement and especially the necessity to calibrate before measurement interferes. For more accurate readings, it is necessary to divide the range of measured tolerance into several sub-ranges, which makes the reading very confusing. A semi-automatic bridge can also be used for resistance measurements

BM 539, This instrument has sufficient accuracy for absolute resistance measurement, but a fairly large error in tolerance measurement - about 1% at 10% tolerance. Another disadvantage is the analog output and the resulting need to connect a digital voltmeter for more accurate reading. is the use of an AC voltage to measure resistances, which is, for example, contrary to the standard in the output control of resistors.

These shortcomings are overcome by a circuit for the numerical tolerance measurement of resistors according to the invention, in which two parallel branches of the active bridge are connected to the normal voltage source, with the first branch connected to the normal voltage source at the input of the first opamp. The object of the invention is that the output of the second operational amplifier is connected to the comparator input over a decade of resistance, while in the second branch of the active bridge it is connected to a normal voltage source. A precision analog inverter is connected to which is connected in series a digital resistor string, the output of which is connected to the comparator input, while the output of the comparator is connected to the control input of the second output of the register is connected via a digital inverter to a decoder whose output is connected to a display device, and the third register output is connected to a second input of a digital inverter and simultaneously to a second input of a display device. The technical advancement of the circuitry for the digital tolerance measurement of resistors according to the invention is that it allows measurements to be avoided by complicated logic for tolerance calculation. Compared to analog measuring methods and tolerance display it is characterized by high resolution, high measuring speed and digital data output for possible further processing.

The invention will now be described in more detail with reference to the accompanying drawing, in which a block diagram for digital tolerance measurement of resistances is shown.

The normal DC voltage source 1 is connected to the input of the first operational amplifier 3 via a normal resistance 2, which serves to adjust the order of the measured resistance 4, to the input of the first operational amplifier 3. The measured resistance 4 is connected in the feedback of this first operational amplifier. an input resistor S to the input of the second operational amplifier 6, which is bridged by a feedback resistor 7 to adjust the gain of the second operational amplifier 6 so that its output voltage is always within the same limits, for example 1 to 10 voilt. Between the output of the second operational amplifier 6 and the input of the comparator 9 there is a resistor decade 8 used to adjust the mantissa of the measured resistance 4.

In the second branch of the active bridge, a precision analog inverter 10 and a digital resistor string 11 are connected in series, the output of which is connected to the same comparator input 9 as the resistance decade 8.

The output of the comparator 9 is connected to the control input of the register 12, the first output of which is connected to the buffer input of the digital resistor chain 11 and the second output is connected via a controlled digital inverter 13 to the decoder 14 whose output is connected to the display device 13. it is connected to the second input of the digital inverter 13 and simultaneously to the second input of the display device 13.

As mentioned above, one branch of the active bridge is set by a normal resistance of 2 order and a resistance decade of 8 mantissa of the measured resistance 4. The second branch is aligned with the digital resistance string 11 in the additional code from state 1 — x to state 1 + x. measured tolerance. When stopping the 1-x digital resistor chain 11, the code inverts to create a negative number, and when the 1 + x state resistor 11 is stopped, mantissa is used as a positive tolerance after subtracting the sign bit.

The digital resistor chain 11 is controlled by the register until the equilibrium of current Ϊ1 of the first active bridge branch and current 12 of the second active bridge branch. This is registered by the comparator 9, which stops the next shift of the register 12. After the following expressions are introduced:

Rx = rx. 10 ^s Rn - 10 ^at Rd = ro. R Gp + (1 + x) 1

R

Ra

Rb = 10 ^u “ ^s measured resistance 4, normal resistance 2, resistance decade 8, conductivity of digital · resistance chain

11, the ratio of the feedback resistance 7 to the input resistance 5, where the auxiliary symbols have the following meanings: rx is the mantissa of the measured resistance 4, s is the order of the measured resistance 4, u is the normal resistance order 2

R is the selected unit resistance, x is the tolerance of the measured resistance 4,

Uo is the output voltage of normal voltage source 1, is pr, o balanced active bridge:

II + 12 = 0 after substitution for currents:

Rx

Rn

Ra

ΊΰΓ

Uo

Rd - Uo

1 + x 'R

After introducing auxiliary symbols into this relationship:

rx. 10 ^p . 10 ^u '

Uo

10 ^u ro. R and after striking:

rx ro

Uo

1 + x

R

The range of equalizing the conductivity of the digital resistance string 11 is selected from the value

1 (1 — xm] —-— up to (1 + xm) —KK, where xm is the maximum tolerance value of the measured resistance, and xm must be less than 1. The conductivity of the digital resistance string 11 is changed in additional code If the active bridge is equalized in the range of the conductivity of the digital resistance string 11 from (1 - xm) to 1, the output of register 12 in tva219481 is ru, ... A zero in the sign bit causes the controlled digital inverter 13 to switch to the inverse state and at the same time causes the minus sign to illuminate on the display device 15. In the controlled digital inverter 13 the mantissa of the number 12 is inverted. lowest order error, which can be arbitrarily reduced by increasing the number of bits. further, to a decoder 14 which transforms the selected additional code into the code of the display device 15, where this result is shown as a negative tolerance.

If the digital resistance string 11 stops within its conductivity range 1 to (1 + xm), the output of register 12 is in the form Ι, ΥΥΥ. . . Poison-

Claims (1)

Connection for digital tolerance measurement of resistances, in which two parallel branches of the active bridge are connected to the normal voltage source, in the first branch is connected to the normal voltage source a normal resistor at the input of the first opamp with feedback the output is connected to the input resistor of the second operational amplifier bridged by a feedback resistor, characterized in that the output of the second operational amplifier (6) is connected via a resistor decade (8) to the comparator input (9), while in the second branch of the active bridge ) of the normal foot in the sign bit means positive tolerance and the number mantissa passes through the controlled digital inverter 13 unchanged and, after passing through the decoder 14, is displayed as a positive tolerance on the display device 15. The circuitry according to the invention can also be used in automated resistance measurement systems where a system output contact unit is used instead of a display device or in resistor sorting devices where the output tolerance value in the digital comparator is compared with the values entered. This connection can also be used to measure the tolerances of other quantities of components whose parameters can be converted to electrical voltage. a precision analog inverter (10) connected to a digital resistor string (11) connected in series, the output of which is connected to the comparator input (9), the comparator output (9) being connected to the control input of the register (12), the first output is connected to the equalization input of the digital resistor string (11), while the second output of the register (12) is connected via a controlled digital inverter (13) to a decoder (14) whose output is connected to a display device (15); the register (12) is connected to the second input of the digital inverters (13) and simultaneously to the second input of the display device (15).