Tip & How-To about Computers & Internet

Radio Interference affecting the UPS

Erratic operation up to and including load loss due to radio or camera flash operation. Do not operate or let customers operate a radio or a camera flash near the critical power systems, especially if the doors are open. Various manufacturers have recommend not to use these devices near the UPS or other Critical Power Systems.

1. Depending on the physical layout and components used on the control boards, the controls may be affected by an Radio Frequency (RF) signal of relatively low strength at the right (wrong to the control circuits) frequency from a hand held radio.
2. Microprocessor circuits which often have a crystal for clock frequency, may modulate the signal in with the clock frequency and cause the CPU to lock up due to a missed or garbled instruction.

3. Analog circuits with high gains, high impedances, and diodes, may demodulate the RF signal and cause the controls to malfunction.

4. So far, cellular phones have not been detected to cause a problem, but it is still a good idea not to get them too close to the control circuits when in use.

NOTE: Units built for certain military applications must meet RF interference

susceptibility specifications. They have special shielding installed, but

even they may not meet the susceptibility specifications with the doors

opened.

5. It has been witnessed for a UPS to blow inverter fuses when a strobe flash on a camera was charging and the UPS doors were open. The RF from the strobe oscillator caused an inverter bridge to misfire.

6. It has also been seen to knock down a microprocessor controlled UPS when the strobe flashed and caused an EPROM to misread even though the UV eraser window on the EPROM was covered with a label. light still penetrated enough to garble the instruction to the CPU and cause it to lock up.

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