Measurement of Telephone-Weighted Noise Voltage in DC Power Supply Noise Voltage
(1) Definition of Telephone Balance Noise Voltage
The noise voltage value measured by the AC component in the output voltage of the rectification equipment after passing through the telephone balance network specified by the W-junction power grid.
(2) Turtle measuring instrument
The measuring instrument used is the JH5151E high and low frequency noise tester.
(3) Measurement method
Connect the test circuit as shown in Figure 10-2, and the testing method is as follows.
① Turn on the power switch, the power indicator light will turn on, and after preheating for 20 minutes, the stability test can be performed.
② Before testing, the instrument should be self calibrated by placing the frequency switch on the testing frequency band, setting the impedance switch to 750, adjusting the zero potentiometer to make the instrument indicate that the impedance switch is in self calibration, adjusting the self calibration potentiometer to make the pointer indicate 1OdB. After each frequency band conversion test, the above process should be repeated to ensure the measurement accuracy of each frequency band.
③ Press the balance measurement button a/b, set the impedance switch to 600Q, set the level conversion switch to+40dB frequency band switch to telephone weighting, set the time constant switch to 200ms, connect the test line to the balance input socket, and string in an isolation capacitor greater than 10uF.
④ Connect the test line to the output section of the DC screen, adjust the level conversion switch so that the pointer indicates a clear reading, and record the algebraic sum of the pointer reading and the level conversion switch reading, which is the balanced noise voltage value, which should be less than 2mV.
Broadband noise voltage
(1) Definition of broadband noise voltage
The root mean square value of the AC component within a certain frequency bandwidth in the output voltage of rectification equipment.
(2) Measuring instruments
The measuring instrument used is the QZY11 high and low frequency noise tester.
(3) Testing method
The test wiring is shown in Figure 10-2.
After testing the balanced noise voltage mentioned above, set the impedance switch to 75 watts and the level conversion switch to+10dB. Connect the test line to a coaxial input socket and set the frequency band switches to 3kHz-150kHz and 150kHz-30MHz respectively. Adjust the sensitivity of the level conversion switch until the meter indicates a clear reading. The test value should be the algebraic sum of the reading on the meter head and the reading on the level switch. When testing in an environment with severe electromagnetic interference, the two ends of the test line should be connected to non-polar capacitors of O.lpF.
