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5. The Technical Means of Diagnostics and Balancing.

Question 5.5.

What type of adapter is it necessary to set for DC-11 in different cases when you set the "Adapter Type" in the dialog window? What adapter is it necessary to set when the vibration sensor or the tacho probe are used?
(The question was asked by the mechanic, responsible for machine diagnostics, Sergej Reshetkin from the joint-stock company "SeverStal")

The question is answered by Vladimir V. Malakhov:

The DC-11 data collector has two inputs to measure the electric values - the linear input connector and the tacho probe connector. As the transducers of physical values, that are used in the industrial applications, can have different types of output signals (for example the electric current or electric charge), VAST, Inc. uses different types of adapters to match the output circuits of the transducers with the input circuits of the data collector.

The adapters are mounted in miniature cases, the output connectors of which are connected with the linear input connector of the data collector. After this the case of the adapter is fixed on the instrument's case by the help of special screws. The main assignment of the adapter is to convert the sensor's sensitivity to the physical parameter in such a way that its dimensionality in the adapter output connector has to be in the units of electric voltage, corresponding to the unit of the physical parameter, and the amplitude of the voltage has to be proportional to the value of the physical parameter. This ensures that the real value of measured physical parameter is calculated by the data collector program (or the diagnostic module of the basic computer) according to the following expression:
 

A=U/S [a],


where


A - is the value of the physical parameter,
U - is the value of the adapter output voltage,
S - is the output sensitivity of the sensor
a - is the unit of the physical parameter.

In principle, if we supply the DC-11 data collector with corresponding transducer it can measure any physical parameter (temperature, pressure, illuminance and so on), but as the VAST, Inc. diagnostic methods are based on the machine vibration characteristics our main attention is paid to the use of adapters for the following vibration sensors:

  • The piezoelectric accelerometer with internal voltage amplifier type AP- 57. Its sensitivity is specified in mV/g and is in the range from 25 to 100 mV/g.

  • The piezoelectric accelerometer without internal voltage amplifier the output signal of which is in the form of electric charge and the sensitivity is measured in pC/g. The data collector DC-11 is supplied with such accelerometer AP-54 and its sensitivity is in the range of 20 - 25 pC/g.

  • An ICP accelerometer - it can be any vibration transducer that meets the requirements to the ICP standard.

The sensitivity of such transducers, that are used in the world practice, can be in the range from 10 mV/g till 10 V/g, depending on the frequency band and the range of values of the oscillation acceleration.

The connection of the vibration sensor to the linear input of the DC-11 is made via a matching device (adapter) - a unique one for each of the three mentioned sensor types. The gain factor of the adapters are equal to 1, so it is possible to use the specified sensitivity of the sensors with all the settings.

The adapter of the vibration sensor AP-57 is a voltage amplifier with the gain factor 1. It includes the output circuit of the sensor internal amplifier and the power circuit.

The charge sensor adapter is a charge amplifier with the gain factor

So, if the sensitivity of the accelerometer is

it ensures the resulting sensitivity:

It should be noted that the amplifier ensures that it is possible to use any type of charge piezoelectric accelerometer with known specified sensitivity if it is provided with the cables that connect it with the adapter.

The adapter for ICP vibration transducer, that has the gain factor 1, is in compliance with the international standards for the stabilized current and voltage internal power adapters.

The setups of the vibration transducers' parameters and corresponding adapters are set in the dialog windows "Choose transducer" and "Changing sensor type" of the DC-11. When setting you should bear in mind the following:

  • The accelerometers are used to measure the parameters of the vibration. The velocity and displacement are calculated by the program using the measured values of the acceleration.

  • The specified sensitivity is used to set up the sensitivity of the accelerometer. The dimensionality is set as mV/g - it means that the sensitivity is set as the output sensitivity of the adapter.

  • The 16 channel adapter is used in some certain cases, for example for measurements during machine balancing.

  • The sensor name "Unknown" is used to configure a new type of sensor. (See "DC-11 User Guide").

 

The transducers and sensors parameters supplied by VAST, Inc. must be set up according to the following table:

 

The "Tacho" input connector is used to receive the signals from the infra red photo transducer designed by VAST, Inc. This transducer is connected directly to the "Tacho" input connector without any adapters.

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