Agilent Measuring High Voltages using the U8903A Audio Analyzer - Application Note 5991-1465EN c20140723 [4] free download

File name Measuring High Voltages using the U8903A Audio Analyzer - Application Note 5991-1465EN c20140723 [4]

Keysight Technologies Measuring High Voltages using the U8903A Audio Analyzer Application Note This note shows how the U8903A-109 BNC accessory kit can be used to make an attenuator that will extend the input voltage range of the U8903A to 300 vRMS. 02 | Keysight | Measuring High Voltages using the U8903A Audio Analyzer - Application Note The U8903A Audio Analyzer can measure a maximum of 140 vRMS on the unbalanced BNC connection. This is more than adequate for most applications but some situations do need to extend beyond this limit. This note shows how the U8903A-109 BNC accessory kit can be used to make an attenuator that will extend the input voltage range of the U8903A to 300 vRMS. An example is shown in Figure 1. Attenuator Attenuation can be achieved in many ways depending on the requirements. For this application there are two main requirements. The first is that that attenuator must have a high input impedance otherwise power dissipation and voltage drop will be too high. The second requirement is that the attenuator must have low output impedance so that it does not from a low pass filter with the input capacitance of the U8903A. The `L' type attenuator is best suited to this application and the schematic is shown in Figure 2. Input 100 kOhms 3.3 kOhms 100 kOhms 100 pF Attenuator U8903A Figure 2. The requirement for high input impedance and low output impedance mean that the attenuator will naturally be of high value, the values shown result in attenuation value of a little over 30 dB. Component Choice The 100 k resistor will be dissipating 0.85 W with a 300 vRMS input. A 1 W metal film 1% tolerance device is the best choice here. For the 3.3 k resistor power is not such an issue but physical size is important. A 0.125 W metal film 1% tolerance device is most suitable. The 100 k resistor in this particular example was from Vishay Dale, model number CCF60. The 3.3 k was from Multicomp, model number MF12. 03 | Keysight | Measuring High Voltages using the U8903A Audio Analyzer - Application Note U8903-83401 BNC Accessory The U8903A-109 BNC accessory kit is used to house the attenuator components as shown in Figure 3. Application note 5991-1466EN should be referred to for assembly instructions. Given the high voltage application care should be taken when positioning and soldering the resistors. Some heat shrink tubing may be beneficial on the ground lead of the 3.3 k resistor. Figure 3. Measurement Compensation With the attenuator connected to th