Larson Davis 824 User Manual

12-14 824 Reference Manual 9/29/09
will perform a calibration and calculate that the level we
measure should be
Lv = 20Log
10
[1.0/(1.0 X 10
-6
)] = 120 dB.
Thus, prior to performing the calibration using the
calibration item in the Tools menu, we set the Cal. Level to
120.
Similarly, should we wish to use the same calibrator to
measure in units of dB relative to 1 µm, we would set the
Cal. Level to
Lv = 20Log
10
[9.86/(1.0 X 10
-6
)] = 139.9 dB
Displaying Amplitude in Linear Units
Providing a digital readout of the
measured amplitude at the cursor
position in linear units.
Although the measured level is always displayed in decibels
on a logarithmic scale with a digital readout at the cursor
position in dB, a second digital readout can be created which
will show the amplitude in linear units. This is particularly
useful when using an accelerometer and desiring to readout
the amplitude in units such as g, m/s
2
, ft/s
2
, etc.The accuracy
of the linear units value will be +/- 5 % of the true value.
This procedure requires evaluating the sensitivity of the
transducer in decibels relative to volts. The sensitivity of the
transducer is usually provided in the manufacturers
specifications. To convert sensitivity to decibels use the
following formula:
When the linear scale is set to zero
the 824 will read the rms input
voltage.
Linear Scale (dB) = 20Log (1 volt / sensitivity)
Obtaining a readout in units of “g”. Example: The sensitivity of an accelerometer is typically
provided in units of V/g. Using an accelerometer having a
sensitivity of 50 mV/g, the Linear Scale would be calculated
as follows:
+26.0 dB = 20Log [1 volt / 0.05V]

Larson Davis 824 Specifications

General

Brand	Larson Davis
Model	824
Category	Measuring Instruments
Language	English