1.2 Metrological indicators of measuring instruments

1.2.1 Physical properties and quantities

Any object of the world is characterized by its properties. A property is a philosophical category and in its essence is a qualitative category.

Value is a property of something that can be distinguished among other properties and evaluated in one way or another, including quantitatively.

Physical quantity is a property that is common in a qualitative sense for a variety of objects, physical systems, their states and the processes occurring in them, but individual in quantitative terms for each of them. The qualitative side of the concept of “physical quantity” defines its “gender” (for example, electrical resistance as a common property of electrical conductors), and the quantitative one - its “size” (resistance of a specific conductor under study). The numerical value of the measurement result depends on the choice of a unit of physical quantity.

1.2.2 Main indicators

The measurement range is the range of values ​​of the measured value, for which the permissible errors of the measuring instrument (measuring means) are normalized.

The measurement limit is the largest or smallest value of the measurement range.

The range of indications is the marked area of ​​the scale, limited by its initial and final values, i.e. indicated by the smallest Xmin and maximum Xmax possible values ​​of the measured value (it can be wider than the measurement range).

The range of operating frequencies (frequency range) is the frequency band within which the instrument error obtained by changing the signal frequency does not exceed the permissible limit.

Calibration characteristic - the relationship that determines the ratio between the signals at the output and the input of a measuring instrument in a static mode.

The sensitivity of the measured parameter is the ratio of the change in the signal at the output of the measuring device to the change in the measured value that caused it:

S = lim ∆ y ,

∆ x (1.6)

where x is the measured value; y is the output signal; ∆x - change

measured value; ∆y is the change in the output signal.

Resolution (absolute) - the minimum difference between the two values ​​of the measured homogeneous quantities, which can be distinguished by the instrument.

Speed ​​(measurement speed) - the maximum number of measurements per unit of time performed with a normalized error.

Input resistance (full) ZBX - resistance of the measuring device from the input terminals. At relatively low frequencies, the input circuit of the measuring device, connected in parallel to the circuit being measured, is represented by an equivalent electric circuit consisting of a RBX resistor connected in parallel and a CBX capacitor. In order not to affect the circuit being measured, devices must have i large active input resistance Rin and a small input capacitance CBX. Therefore, in the low-frequency region, ω = 2πƒ, when the capacitance is large compared with the active resistance 1 / (ωСвх) >> Rвх, the input resistance of the measuring device is almost ZBX = RBX. In the high-frequency region, the input impedance of the device is determined mainly by the capacitance and ZBX = 1 / (jωСвх), since 1 / (ωСвх) << RBX.

Output resistance ZВХ - resistance of the measuring device from its output terminals. This resistance determines the permissible load of the measuring device when it is connected, for example, to a computer.

Own power consumption Rsob, the power consumed from the circuit being measured (the less Rsob, the more accurate the measurement).

The errors of the measuring device - instrumental errors.

Test questions:

1. What is a measurement tool?

2. What are the signs classify measuring instruments?

3. Give examples of measuring instruments of various physical quantities.

4. What are the measuring devices?

5. What are the signs classify measuring devices?

6. What are the parameters and characteristics described modern measuring devices?

7. What is a measuring system?

8. For what purposes are information-measuring systems, measuring-computing complexes and computer-measuring systems intended?