RCA AC Power Line Monitor - Models WV-120A - Tested
RCA AC (RMS) Power Line Monitors - Model WV-120A - Unit has been tested. Easy to use. Simply plug in. This instrument provides continuous, accurate indication of the AC line at a glance, without the inconveniences of handling probes and switches or the necessity of selecting one of several scales to determine the proper meter reading. Procedure to calibrate and operate below.
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The meter movement in the WV-120A is a moving-vain type which indicates RMS values even when the waveform of the power-supply voltage is distorted. (Peak reading and peak-to-peak reading AC voltage measuring circuits, such as used in conventional VTVM's are calibrated on the basis of pure sine-wave voltages, and such meters do NOT indicate the true RMS value of distorted waveforms.) The meter movement is only slightly damped and therefore has fast response. This feature is highly desirable because it permits the meter to indicate the presence of line-voltage "bounce" or fluctuations. Since the WV-120A utilizes a moving-vain type meter, it is necessary that the instrument be kept away from strong magnetic fields, such as those developed by power transformers.
To use the WV-120A, simply plug the line cord into the AC outlet and allow at least 5 minuets for warm-up. The meter pointer will indicate the RMS voltages of the AC power line. The instrument may be left on permanently, providing a continuous indication of the power-line voltage. To prevent static charges from forming on the meter case which would affect the operation of the meter, the clear plastic meter case front has been treated with anti-static solution.
The WV-120A is carefully calibrated at the factory in comparison with dynamometer-type laboratory standard reference meters. If recalibration is required, the WV=120A should be sent to the nearest authorized RCA Test Equipment Repair Stations. These stations are equipped with the necessary precision reference standards.
Note: As a safety precaution, it is recommended that an isolation transformer be used during this calibration procedure.
1. Remove the two screws on the rear of the instrument, then lift off the back cover by pulling it downward from the case.
2. Connect the WV-120A, together with a secondary standard reference meter with an accuracy of +/- 0,25%, to a variable AC power source. Allow at least five minuets for the WV-120A to warm up.
3. Set the voltage source at exactly 120 volts as indicated on the reference meter. Adjust the variable 500 ohm resistor R1 so that the meter reads 120 volts.
4. Set the voltage source at 100 volts as indicated on the reference meter. Carefully insert a soldering tool or similar pointed device through the small hole in the front of the meter. Engage the slotted adjustment lever, then move the lever slightly sideways as required to bring the WV-120A meter pointer to 100 volts.
5. Again set the voltage source at 120 volts, as in step #3 above. If necessary, reset the adjustable 500 ohm resistor so that the WV-120A meter reads exactly 120 volts.
6. Repeat steps 3, 4 and 5 if necessary and check accuracy at 140 volts. Slight compromises may be required at higher end of the scale, or at the center, to obtain maximum accuracy throughout the range of 100-140 volts. Before reassembling the case, make certain that the terminals of the resistor are not shorting against the metal case of the instrument.