HT instruments HT157 - Manual (Page 37)

HT155 - HT157
EN - 35
6. INSTRUMENT ACOUSTIC CALIBRATION
6.1.1. FOREWORD
The instrument is regularly calibrated upon purchase and upon first use. The acoustic
calibration of the sensitivity level of the microphone is recommended in order to always
carry out correct tests at the beginning of each measuring campaign and must be carried
out by using the provided portable calibrator in Class 1 HT151, with an operating
frequency of 1kHz
 1% and harmonic distortion <1%.
6.1.2. PRELIMINARY OPERATIONS
Select the “Calibrate” icon in any measuring mode and confirm with “ ”. The instrument
displays the following screen:
 Line 1
 Line 2
 Line 3
 Line 4
 Line 5
 Line 6
Fig. 35: Initial screen of calibration section
Line 1
This line contains the serial number of the microphone, which is a read-
only datum, not modifiable by the user
Line 2
This line contains the field relevant to the free-field correction of the
microphone on the sound-level meter. To use the instrument with ½”
microphones, this parameter is 0.15dB at a frequency of 1kHz. To
change this value, proceed as follows:
 Use the keys “ ” or “ ” to select “Mod.” and confirm with “
”. The
“Mod” field appears highlighted
 Use the “ ” or “ ” keys to move the cursor to Line 2 and the “ ” or
“ ” keys to define the value in steps of 0.1dB. Accordingly, also the
“App” field is highlighted
 Move the cursor to the “App” field and press “
” to confirm
Line 3
This line contains the indication of the output sensitivity level of the
preamplifier of the microphone used by the instrument. The microphone
may need to be calibrated again in case the preamplifier is replaced,
because of the different gain and input capacitance values. Proceed as
follows:
 Use the keys “ ” or “ ” to select “Mod.” and confirm with “
”. The
“Mod” field appears highlighted
 Use the “ ” or “ ” keys to move the cursor to Line 3 and the “
” or
“ ” keys to define the value in steps of 0.1dB. Accordingly, also the
“App” field is highlighted
 Move the cursor to the “App” field and press “ ” to confirm