1. Selecting Fuse Resistors: Fuse resistors, balancing protection and performance, demand careful consideration. Key is to select resistance and power parameters tailored to the circuit's specific needs. It's crucial that they fuse quickly under overload yet maintain stable, long-term operation under normal conditions. Overly high resistance or power values fail in providing adequate protection.
2. Choosing Fixed Resistors: Fixed resistors come in a plethora of types. The choice of material and structure should align with the application circuit's unique requirements. High-frequency circuits favor non-wirewound resistors like carbon film, metal, and metal oxide film resistors, due to their low distributed inductance and capacitance. For high-gain, small-signal amplification circuits, low-noise resistors such as metal film, carbon film, and wirewound resistors are preferred, steering clear of noisy synthetic carbon film and organic solid resistors. Wirewound resistors, though larger, offer greater power, less current noise, and high-temperature resistance. They're typically used in low-frequency circuits or as current-limiting, voltage-dividing, bleeder, or bias resistors for high-power tubes. Precision versions find use in attenuators, resistance boxes, computers, and precision instruments. Always choose a resistance value close to the nominal value required by the circuit, prioritizing standard series resistors. General circuits can accommodate ±5% to ±10% resistor error, but precision instruments and special circuits need precision resistors. The selected resistor's rated power must meet circuit requirements, and its power capacity shouldn't be arbitrarily altered. If a power resistor is needed, its rated power could be 1 or 2 times higher than the circuit's actual power requirement.
3. Selecting Varistors: Varistors, crucial in overvoltage protection circuits, come in diverse models and specifications. Key parameters including nominal voltage, maximum continuous operating voltage, maximum limit voltage, and current capacity must align with the application circuit's demands. Accurate nominal voltage is essential: too high and it won't protect against overvoltage; too low, and it risks malfunction or breakdown.
4. Choosing Humidity Resistors: When selecting a humidity-sensitive resistor, first determine the type needed by the application circuit. For high humidity detection in appliances like washing machines and dryers, lithium chloride hygroscopic resistors are suitable; for medium humidity environments in devices like air conditioners, ceramic humidity-sensitive resistors work well. For weather monitoring or video recorder dew detection, polymer hygroscopic or selenium film hygroscopic resistors are apt choices. Ensure the chosen hygroscopic resistor's main parameters (including humidity measurement range, nominal resistance, working voltage) meet the circuit's requirements.
5. Picking Photoresistors: Begin by identifying the photoresistor's spectral characteristic needs for the application circuit. For electronic products like photoelectric control systems, electronic cameras, and light alarms, visible light photoresistors are ideal; infrared photoresistors suit infrared signal detection in astronomy or military applications. For ultraviolet detection, UV photoresistors are the go-to. After type selection, verify that the photoresistor's main parameters (including light resistance, dark resistance, maximum operating voltage, apparent current, dark current, rated power, sensitivity) fulfill the application circuit's needs.