Measurement of sweep voltage non-linearity. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Measuring technology

 Comments on the article

The methods for measuring the error of a device with a linearly varying voltage, presented by the author on the example of an oscilloscope sweep generator, can also be used to assess the quality of other similar units.

The linearly changing voltage (LIN) is used in a wide variety of electronic devices. Most clearly, in the literal sense of the word, it manifests itself as a developing voltage in the horizontal deflection channel of the oscilloscope.

The transformation of an oscilloscope from a device that allows you to visually qualitatively evaluate the shape of the electrical signal under study into an accurate measuring device became possible after the creation of a CRT with a flat screen, an internal parallax-free scale and accurate calibrated sweep generators. In order to determine the duration of the signal under study directly on the scale of the tube, the output voltage of the horizontal sweep generator must be linear and stable. But it is impossible to obtain a linear unfolding voltage without the ability to measure its nonlinearity.

Nonlinearity measurement methods are considered using the sweep generator described in [1] as an example. On fig. 1 shows a simplified diagram of its LIN pulse shaper. The sweep voltage is linearized by changing the voltage transfer coefficient of the follower to VT1, VT2, in which KU = (R2 + R3 + R4) / (R3 + R4).

Judging by the resistance values ​​of the resistors included in the formula, it is very close to 1. When the resistance of the resistor R2 changes from 0 to 5 ohms, the sweep voltage nonlinearity changes its sign and absolute value by a few tenths of a percent.

The article discusses several measurement methods. Their resolution, i.e. the minimum non-linearity that they can measure, reaches 0,02 ... 0,04%.

In the sweep generator, the circuit of which is shown in Fig. 1, the formation of LIN occurs by charging the capacitor Ct with a constant current through the resistor Rt, therefore, the voltage drop across it between points A and B must be constant. Let's denote it as UR. If this voltage is applied to the input of the measuring oscilloscope, then the screen will display, in the first approximation, a horizontal straight line. If KU does not change throughout the LIN, then the line on the screen will be really straight. In the case of a positive non-linearity of the sweep, the right end of the line on the screen will deviate by ΔUR down, with a negative one - up. As a rule, KU is not quite stable, therefore, in the general case, the sweep nonlinearity

ε= ±(ΔUR /UR)x100[%].

It is very convenient to measure UR with an oscilloscope with a differential input. Unfortunately, with a large resistance Rt, significant errors arise: the input resistance of the differential stage of the oscilloscope, connected at point A (let's denote it RBX), shunts the resistor Rt. Usually the value of RBX=1 MΩ. The other input of the differential stage of the oscilloscope does not affect the LIN parameters, since it is connected to the low-ohm output of the repeater at point B.

Nonlinearity can be estimated with good accuracy with a conventional oscilloscope. The measurement scheme is shown in fig. 2. When measuring, the common power rails of the generator and the oscilloscope and their cases must be isolated from each other. Element G1 - to compensate for the constant component, the installation of which is carried out with a tuning resistor R4.

Here, the input resistance of the oscilloscope is connected in parallel with Rt and shortens the LIN pulse somewhat without introducing additional non-linearity. The capacitance of the oscilloscope case in relation to the generator case, as well as the input capacitance of the oscilloscope and the capacitance of the probe cable Свх also do not affect the formation and parameters of the LIN pulses.

Another method for measuring non-linearity is based on the fact that the first derivative of a linearly varying function is a constant value. This means that if the signal from the output of the LIN shaper is fed through the differentiating RC circuit to the input of the oscilloscope, then we will see a horizontal straight line on its screen (at ε = 0). This method is used in practice and is even recommended as an example in the collection of problems for universities [2]. However, in reality, a different picture is obtained on the screen (Fig. 3). Here U1 is a linearly changing voltage, U2 is the expected image of the first derivative, U3 is the real picture.

This method, as it is usually used, is not suitable for assessing the non-linearity of the sweep of the oscillator in question, but there is one artificial trick that allows it to be used. Let's look at fig. 4, a.

A correction resistor RK is connected in series with the capacitor Ct, at a nominal value approximately equal to Rt. When RK > 0, the voltage at point A after opening the key S does not increase from 0, as usual, but jumps - from UK = it · RK. The voltage jump is transmitted to the output of the repeater at point B, and the picture shown in Fig. 4b. The possibilities of this artificial technique are limited by the fact that the beginning of the impulse U2 is, as it were, cut off. If information is sacrificed from 10% of the LIN duration, which is quite acceptable (the initial and final sections of the sweep voltage are rarely used), then U2 = 500 ... 600 mV. The resolution of the method when using, for example, an oscilloscope C1 - 83 with a minimum division value of 0,2 mV, reaches 0,04%.

Without the use of RK, the initial part (10%) of the signal is lost at U2= = 100 mV. The resolution of the method deteriorates to ±0,2%. A valuable property of this method is that it can be used to measure the nonlinearity of the sweep voltage after the horizontal channel amplifier, which cannot be done by other methods.

Another method proposed by V. A. Bondar and V. A. Shaverin [6] resembles the previous one according to the scheme (Fig. 5).

A resistor Rp is connected in series with Rt and Ct, and the signal is taken from it. After opening the key S, a voltage jump occurs on the resistor Rp, as on the resistor RK in circuit 4, a. The greater the resistance of the resistor Rp, the greater the signal value and the higher, it would seem, should be the resolution of the method. However, there are sources of error that limit it. In particular, the resistance Rt forms an integrating circuit with the capacitance (Ck + Cvh). The leading edge of the pulse Up collapses, and part of the measured signal is lost. With a loss of duration of about 10%, the amplitude Up is 500 ... 600 mV and the resolution of the last method is the same.

Literature

1. Dorofeev M. Oscilloscope sweep generator. - Radio, 1996, No. 11, p. 32 - 34.
2. Collection of problems and exercises on electrical and electronic measurements. - M.: Higher school, 1980.
3. Bondar VA, Shaverin VA On one method of measuring the nonlinearity coefficient in LIN generators. - Metrology. 1975, no. 7, p. 63 - 70.

Author: M. Dorofeev, Moscow

See other articles Section Measuring technology.

Read and write useful comments on this article.

<< Back

Latest news of science and technology, new electronics:

Machine for thinning flowers in gardens 02.05.2024

In modern agriculture, technological progress is developing aimed at increasing the efficiency of plant care processes. The innovative Florix flower thinning machine was presented in Italy, designed to optimize the harvesting stage. This tool is equipped with mobile arms, allowing it to be easily adapted to the needs of the garden. The operator can adjust the speed of the thin wires by controlling them from the tractor cab using a joystick. This approach significantly increases the efficiency of the flower thinning process, providing the possibility of individual adjustment to the specific conditions of the garden, as well as the variety and type of fruit grown in it. After testing the Florix machine for two years on various types of fruit, the results were very encouraging. Farmers such as Filiberto Montanari, who has used a Florix machine for several years, have reported a significant reduction in the time and labor required to thin flowers. ... >>

Advanced Infrared Microscope 02.05.2024

Microscopes play an important role in scientific research, allowing scientists to delve into structures and processes invisible to the eye. However, various microscopy methods have their limitations, and among them was the limitation of resolution when using the infrared range. But the latest achievements of Japanese researchers from the University of Tokyo open up new prospects for studying the microworld. Scientists from the University of Tokyo have unveiled a new microscope that will revolutionize the capabilities of infrared microscopy. This advanced instrument allows you to see the internal structures of living bacteria with amazing clarity on the nanometer scale. Typically, mid-infrared microscopes are limited by low resolution, but the latest development from Japanese researchers overcomes these limitations. According to scientists, the developed microscope allows creating images with a resolution of up to 120 nanometers, which is 30 times higher than the resolution of traditional microscopes. ... >>

Air trap for insects 01.05.2024

Agriculture is one of the key sectors of the economy, and pest control is an integral part of this process. A team of scientists from the Indian Council of Agricultural Research-Central Potato Research Institute (ICAR-CPRI), Shimla, has come up with an innovative solution to this problem - a wind-powered insect air trap. This device addresses the shortcomings of traditional pest control methods by providing real-time insect population data. The trap is powered entirely by wind energy, making it an environmentally friendly solution that requires no power. Its unique design allows monitoring of both harmful and beneficial insects, providing a complete overview of the population in any agricultural area. “By assessing target pests at the right time, we can take necessary measures to control both pests and diseases,” says Kapil ... >>

Random news from the Archive Axis P1435-E and P1435-LE HD Network Cameras 19.12.2015 Axis Communications has introduced two new HD network bullet cameras for 1435/1435 video surveillance. The Axis P50-E and Axis P264-LE models use Axis Zipstream technology, which saves bandwidth and disk space by up to XNUMX% or more compared to standard H.XNUMX compression. Thanks to Lightfinder technology, the cameras allow you to get a color image in low light conditions. They also implement a wide dynamic range technology - Forensic Capture (WDR - Forensic Capture), which allows you to control complex contrast areas (for example, brightly lit areas with dark areas). New items are made in a compact lightweight case with a built-in bracket for wall or ceiling mounting. A wide range of mounting hardware is available to simplify installation. Installation of the Axis P1435 E and Axis P1435-LE is made easy with remote zoom and focus, which allows you to fine-tune the image from your computer without going to the camera itself. In turn, the function of counting the number of pixels allows you to make sure that all the established requirements for resolution are met. Support for Axis Corridor Format with a 9:16 aspect ratio allows you to observe narrow spaces such as stairs, corridors, passages and tunnels. P-Iris control for optimum depth of field, resolution, contrast and clarity. The Axis P1435-E and Axis P1435-LE models are equipped with an I/O port that can be used for signaling the alarm panel, relay control and other functions.

Other interesting news:

▪ space tanker

▪ Coffee can change the sense of taste

▪ Tesla Megapack 1,5 MW megabattery

▪ Wind electricity on bacteria

▪ A hybrid of atomic clocks and ultra-precise scales

News feed of science and technology, new electronics

Interesting materials of the Free Technical Library:

▪ site section Power supplies. Article selection

▪ article by Ronald Wilson Reagan. Famous aphorisms

▪ article Are jellyfish dangerous? Detailed answer

▪ article A worker engaged in clearing logging sites. Standard instruction on labor protection

▪ article A simple square wave generator. Encyclopedia of radio electronics and electrical engineering

▪ article Shrinking coin. Focus Secret

Leave your comment on this article:

All languages ​​of this page

Arabic	Hebrew	Polish
Bengali	Hindi	Portuguese
Chinese	Italian	Spanish
English	Japanese	Turkish
French	Korean	Ukrainian
German	Malay	Vietnamese

Home page | Library | Articles | Website map | Site Reviews

www.diagram.com.ua
2000-2024