High-end measuring instruments are composed of many electronic components. During the working process, the heat generated by the electronic components converges, causing the internal temperature of the instrument to rise, resulting in a decrease in the accuracy of the instrument. How does a high-end measuring instrument solve the effect of temperature on its own accuracy?
Temperature affects the performance of electronic components1. Influence on diode volt-ampere characteristics
When the ambient temperature rises, the forward characteristic curve of the diode will shift to the left and the inverse characteristic curve will move down, as shown in Figure 1. At room temperature, the forward voltage drop is reduced by 2~2.5mV for every 1°C increase in temperature; the reverse current is approximately doubled for every 10°C increase in temperature. It can be seen that the characteristics of the diode are sensitive to temperature.
Figure 1 volt-ampere characteristics of the diode
2. Influence on transistor input and output characteristics
Due to the thermal sensitivity of semiconductor materials, the parameters of the transistors are almost always temperature dependent.
Effect of temperature on input characteristics: Similar to diode volt-ampere characteristics, when the temperature rises, the forward offset will shift to the left, and vice versa, as shown in Figure 2.
The effect of temperature on the output characteristics: as shown in the solid line in Fig. 3, the broken lines show the characteristic curves at 20 °C and 60 °C, respectively. It can be seen that when the temperature rises, the collector current increases due to the left shift of the input characteristics.
Figure 2 Effect of temperature on transistor output characteristics
Figure 3 Effect of temperature on transistor input characteristics
Stable static working point to suppress temperature driftAmong the many factors that cause the static working point to be unstable, the influence of temperature on the transistor parameters is the most important. The so-called stable static working point suppresses the temperature drift, which usually refers to the static collector current and tube voltage drop of the transistor when the ambient temperature changes. Basically unchanged, it must rely on the change of the base electrode current to offset the change of the collector current. It is common to use DC negative feedback or temperature compensation to make the base current change opposite to the collector current when the temperature changes.
The necessity of preheating the instrumentDepending on the purpose and precision of the equipment, some require preheating, some do not require preheating, and the equipment is preheated for thermal stability of the internal electronics. Capacitors, inductors, transistors, etc. in the circuit reach a steady state and require a certain amount of time. They must be preheated to reduce the measurement error. The more precise the equipment, the longer the preheating time.
How can the Zhiyuan Electronic Power Analyzer make the measurement results more accurate:
1. Preheat the instrument before using the instrument;
2. Before the measurement starts, the zero adjustment operation is required. Zero adjustment refers to the state in which the input signal is zero in the internal circuit of the power analyzer, and the calculation result in this state is set to the zero level in the numerical sense. the process of;
3. Choosing the right range, update rate, and synchronization source is critical to the measurement accuracy of the power analyzer. For example, when the update period is less than the measured signal period, as shown in FIG. 4 below, the data in the entire update period becomes the measurement interval, and the sample data in the entire update period will be averaged, thus affecting the accuracy of the measurement result. In this case, it is necessary to increase the update period so that the measured signal containing more cycles enters the measurement interval;
Figure 4 update cycle comparison
4. Reduce the influence of stray capacitance on the measurement result, because there is insulation relationship between the instrument case and the shielding box of the internal measurement circuit, so there is stray capacitance between the two, and the current measurement circuit is connected to the low voltage side, such as As shown in Figure 5, when the current input terminal of the instrument is connected to one end close to the ground potential of the power source, the influence of stray capacitance on the measurement accuracy can be effectively reduced;
Figure 5 wiring diagram
5. To reduce the influence of power loss, in the case of measuring large current, the voltage measurement loop needs to be connected to the side close to the load. The result measured by the current measurement loop is the sum of the current flowing through the load and the voltage measurement loop. The measurement error is only It is the current flowing through the voltage measurement loop. In the case of measuring small current, the current measuring circuit needs to be connected to the side close to the load. The result measured by the voltage measuring circuit is the voltage of the load voltage and the current measuring circuit, and the measuring error is only the voltage across the current measuring circuit; As shown in Figure 6.
Figure 6 Wiring diagram at different currents
At the same time, Zhiyuan Electronics' PA power analyzer adopts 100M synchronous clock with high stability temperature compensation to ensure the phase synchronization of each channel of ADC sampling, and the phase error of voltage and current is within 10 ns. In the module control unit of the host part, we use a 100M synchronous clock with high stability temperature compensation. This clock signal will be sent to the ADC of each channel to ensure the phase synchronization of the ADC sampling, the voltage between the single channel and the channel, The current error can be guaranteed within 10 ns, and the U and I angles are introduced into the instrument itself to reduce the error, ensuring the active power and power factor measurement accuracy! There are many problems in the industry that the power factor is over 1, or too low to be accurately measured. It has a great relationship with the introduction error and test method of the instrument itself. Before the introduction of Zhiyuan Electronic Power Analyzer, the early instruments basically relied on post-calibration instead of hardware synchronous clock source, which was due to advances in electronic technology! As shown in Figure 7.
Figure 7 PA power analyzer architecture
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