Single Phase Frequency Converters 50/60 Hz
18 models 1KVA to 20KVA
50 or 60hz input,
50hz or 60hz output
Single Phase Frequency Converters 400hz
18 models 1KVA to 20KVA
50hz or 60hz input and
400hz output
Three Phase Solid State Frequency Converters
50 or 60 Hz
57 models 10 to 320KVA
Three Phase Solid State Frequency Converters
57 models 10 to 320KVA
Solid State Design Considerations Manuals and Connection Diagrams Accessories
Outdoor Enclosures, Carts,
Distribution Panels etc.
Notes and Photos
Rotary 1 or 3 Phase Frequency Converters
50 or 60hz output
6KVA to 2000KVA
Rotary 400Hz output Frequency Converters
1 or 3phase
10KVA to 250 KVA
Rotary Frequency Converters Accessories
Enclosures (Indoor quietized and Outdoor) Digital Meters, RS232 and Data Logging, etc.
Rotary Design Considerations Starting Surge of motors in the load, Large SCR loads, power factor and resistive loads, Operating Noise Level.
Rotary Application Notes and Photos Operating Noise and solutions to this problem Line Isolation Sets
  Visicomm Industries
Solid State Frequency Converter Rotary Frequency Converter

Decibel  (dB)


Sounds can be measured using absolute units of energy or pressure, e.g. watts per unit area or millibars, but these numbers become very large and impractical. Thus the Decibel (dB) system was developed. Sound is expressed in terms of logarithmic ratio between two values, usually the intensity or pressure of the sound being measured and a reference intensity or pressure. The formula for calculating a logarithmic ratio, or level, in decibels is expressed as:

dB = 101og 


Using the logarithmic ratio we can compress the entire range of audible sound pressure into a convenient scale of 0 to 140 dB.

Common Sounds

This decibel (dBA) table compares some common sounds and shows how they rank in potential harm to hearing. In many industries, workers are exposed to dangerous noise levels. This is particularly true in the construction, lumber, mining, steel and textile industries.

Boom Cars 140  
Jet Engines (Near) 140  
Shotgun Firing 130  
JET TAKEOFF  (100-200 Fl.) 130  
Rock Concerts (Varies) 110-140 Threshold of Pain  (125 dB)
Oxygen Torch 121  
Discotheque/Boom Box 120 Threshold of Sensation  (120 dB)
Thunderclap (Near) 120  
Stereos (Over 100 Watts) 110-125  
Symphony Orchestra 110 Regular Exposure of more than 1 minute risks permanent hearing loss  (over 100 dB)
Power Saw (Chain Saw) 110
Jackhammer 110
Snowmobile 105  
Jet Fly-over (1000 Ft.) 103  
Electric Furnace Area 100 No more than 15 minutes of unprotected exposure recommended (90-100 dB)
Garbage Truck / Cement Mixer 100
Farm Tractor 98
Newspaper Press 97  
Subway / Motorcycle (25 ft.) 88 Very annoying
Lawn Mower / Food Blender 85-90 Level at which hearing damage (8 hrs.) begins   (85 dB)
Recreational Vehicles / TV 70-90  
Diesel Truck (40Mph, 50 Ft.) 84  
Average City Traffic Noise 80 Annoying;  interferes with conversation; constant exposure may cause damage
Garbage Disposal 80  
Washing Machine 78  
Dishwasher 75  
Vacuum Cleaner 70 Intrusive; interferes with telephone conversation
Hair Dryer 70
Normal Conversation 50-65  
Quiet Office 50-60 Comfortable  (under 60 dB)
Refrigerator Humming 40  
Whisper 30 Very quiet
Broadcasting Studio 30  
Rustling Leaves 20 Just audible
Normal Breathing 10  
  0 Threshold of normal hearing  (1000-4000 Hz)

Since the sensitivity of the ear to sound is not the same for all frequencies, weighting or attenuating filters are included in the sound level meter's circuits to simulate the ear's response.  A noise level meter gives an instantaneous measurement of the noise present, but cannot measure the duration of the exposure.   To measure the amount of noise a person is exposed to over a period of time, a "dosimeter" or an integrated sound level meter must be used.  Sources for above include the American Medical Association and the Canadian Hearing Society of Ontario.  Decibel table developed by the National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, Maryland 20892.   January 1990.

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