I am a technician who repaired Chadwich-Helmuth equipement for 17 years. I have not seen scientific-Atlanta or Microvib but have certainly heard of it and seen the pictures. If you want to know why Bell bought Scientific-Atlanta, it was politics and nothing else. Chadwick wanted to keep the propriatary rights to their software and Bell had other ideas. That is all I will say on the subject.
Here is a quick lesson on vibration transducers so you can teach this to your students. There are three types of vibration transducers, the accelerometer which most are familiar, the velocimeter and the high temperature accelerometer. So lets start with the accelerometer. Chadwick and a few other companies manufacture thise device. If you pull one of these things apart you will find a quartz crystal sandwiched between the base and a cylidrical weight. The quartz crystal pricipal is a recogized one, when you squeese it it gives off an electrical charge just like your solid state cigaret lighter gives off a spark.
OK now when you vibrate this thing it will give you an output in amplitude and frequency. The faster you vibrate it will increase the frequency and the harder you vibrate it will increase the amplitude. These transducers are of course direction sensitive. These transducers are also very broadband, they will transmit all frequencies between zero and 10,000 rpm. All the balancer does is to isolate the frequency of interest and give you a amplitude and phase if you have a mag pickup.
The problem with other accelerometer manufacturers except Chadwick is the tolerance of the amplitude output. Chadwick's accelerometers maintain a plus or minus 10 percent error throughout their range. I have not found an off the shelf accelerometer that can duplicate this. This is why Chadwick makes their own accelerometers.

Velocimeters. A velocimeter differs from an accelerometer phisically by a threaded connector instead of a bayonetted connector and it has four pins instead of three. Other than that it is identical. Velocimeter technology is a little complicated but not overly. The three connections to an accelerometer are +9 to 12 volts power, signal output and ground. These units have a small amplifier in the barrel. They amplify the crystal output to the balancer. The raw imformation was integrated in the balancer to give a usefull reading.
This worked fine for frequencies below 10,000 rpm because the balancer could handle the high outputs. When you get above these frequencies the acceleration component of the vibration overloads the amplifier circuitry and floods the balancer. When Chadwick wanted to move into higher frequency troubleshooting they had this problem. The velocimeter solves this problem by integrating the high frequencies inside the velocimeter. This necessitated a fourth input to the Velocimeter, a negative 9-12 volt line to power the integrator. This conversion from an acceleration curve to a velocity curve is what the velocimeter does. Hardware wise it meant less components in the balancer so if you payed more for your velicimeter balancer than your old one then thats too bad.

High temperature accelerometers are used on the hot sections of turbine engines. These devices are just moving magnets inside coils. These units are calibrated by the manufacturer and have a calibration factor supplied. You have to dial this factor on your equipment before taking readings because it has an effect on gain. These readings must be accurate because you have to submit them to engine manufacturers such as Turbomecca to maintain your warranties. We use to modify 192A spectrum analyzers to read spoolup vibrations on turbines but I dont know if it is still done.

If your head is spinning then send some questions, I seem to be able to generate lots of threads!!

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