Online testing technology plays a crucial role in overcoming the limitations of traditional offline testing, which is often time-consuming and inefficient. By enabling real-time monitoring and diagnosis, it significantly enhances the maintenance quality of modern electronic systems. One of the key challenges in online testing is the measurement error caused by the parallel effect. This phenomenon occurs when additional resistances are unintentionally connected in parallel with the component being tested, leading to inaccurate readings.
To mitigate this issue, several techniques can be employed. However, for testing discrete components, the Guauding method stands out as a cost-effective and efficient solution. The core idea behind this approach is to isolate the component under test from any shunt paths during the measurement process. In practice, this means treating the circuit under test (R) along with the shunt elements at both ends as two parallel resistors, R1 and R2, as illustrated in Figure 1. By ensuring that one of these resistors, say R1 or R2, carries no current—effectively acting like an open circuit—the shunt effect is eliminated, allowing for more accurate resistance measurements.
As shown in Figure 2, the shielding technique leverages the properties of operational amplifiers. Here, R1 and R2 represent the equivalent resistances at the test points A and B, while the constant current source is represented by Rr. Due to the virtual ground concept in op-amps, the inverting input terminal is at the same potential as the non-inverting terminal. This ensures that almost all the current flows through R, effectively bypassing the shunt resistance. As a result, the measured voltage accurately reflects the value of Rx, provided the current I is appropriately set.
The ICL7107/7106 is a dual-integration analog-to-digital converter designed to directly drive LED or LCD displays. It features a variety of pins, each serving a specific function. For instance, pins 40, 39, and 38 are connected to the clock generator components, while pin 37 acts as a test terminal. When shorted to V+, it lights up all the segments of the display. Pin 36 and 35 are used for reference voltage input, and pins 34 and 33 connect to the reference capacitor. Pin 32 serves as the common analog ground, and pins 31 and 30 are the analog voltage input terminals. Additional pins handle functions such as self-zeroing, buffer output, integrator connections, power supply, and digital ground.
The test circuit, as shown in Figure 3, includes a resistance-voltage conversion circuit (dotted line A) and a 555 timer circuit (broken line B) operating in an astable mode to generate a square wave. This square wave powers the ICL7107’s 26th pin at 3.4V. Probes 2 and 3 are connected across the resistor under test, while probe 1 is selected based on the actual circuit configuration. Using a CMOS operational amplifier in a deep negative feedback configuration improves the accuracy of the system.
Experimental results confirm the effectiveness of this method. As shown in Table 1, when properly configured, the measurement error for resistances ranging from 100Ω to 10MΩ remains within 5%, meeting the stringent requirements of modern electronics maintenance and inspection.
Error analysis reveals that the open-loop voltage gain of the operational amplifier significantly affects measurement accuracy. Although high gain is desirable, it is not infinite, leading to minor differences between the input terminals. To minimize this error, an op-amp with a higher open-loop gain should be used. Additionally, the input current of the op-amp can cause shunting, reducing measurement precision. Therefore, selecting an op-amp with high input impedance—such as a CMOS device—and adjusting the constant current source accordingly helps improve accuracy.
NiCoMn Lithium Battery
Ncm Battery,Lithium-Ion Battery With Ncm Material,18650-2800Mah Battery,Nicomn Lithium Battery
Henan Xintaihang Power Source Co.,Ltd , https://www.taihangbattery.com