Norsonic nor140 Instructional Manual Download Page 37

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Norsonic Nor140

Instruction Manual

Microphone check.

For long term monitoring purposes, it is often handy to be able to check the func-

tionality of the measurement system along the signal line from microphone/preamplifier until the display
of the instrument without the use of an external calibrator. The Nor140 has a build-in Mic.Check feature

that allows this (also called SysCheck).

Pin 1 on the microphone input socket is able to supply a known voltage signal to the Norsonic Preamplifier

Nor1209 (see Chapter 28 for details). By enabling this constant voltage signal, the entire measurement chain includ-
ing the microphone is tested, and the display will show the corresponding measured value in dB. Hence, if this
value is constant from the previous check, it is highly likely that the overall functionality of the measurement chain
is constant.

The procedure for using this Mic.Check feature is as follows:

1. Perform a normal calibration of the entire instrument by use of an external calibrator (see the previous

pages in this Chapter 3 for details)

2. Press the

SETUP

(Instr.) >

(Misc.par.) >

(Mic.chk.) key sequence to open the Mic.Check menu. Place

the cursor on the upper field, and turn the feature “ON” by use of the

INC

DEC

keys.

3. If an external device simultaneously should be controlled by the Mic.Check feature, turn the DO-3 (Digital Output

line 3) “ON” in the lower field instead. This is the case when using outdoor microphone Nor1210 A or C.

4. Exit from the Mic.Check menu by pushing the

ENTER

key four times.

5. By pushing the

CAL

key, the Mic.Check signal is activated. The measured signal is then read in the display. The

level will be dependent of the actual previous sensitivity calibration as well as the individual preamplifier and
microphone in use. Normally, using the Norsonic Preamplifier Nor1209 and Microphone Nor1225, the level will
be approx. 90 dB with a 1-2 dB variation from instrument to instrument.

6. Push the

CAL

key again to turn off the Mic.Check feature, and make the normal measurements.

7. At any time, both during and after a measurement (i.e. Running or Ended/Stopped status), the Mic.Check feature

may be turned on again. The level should display the same value as read in point 4 above.

NOTE/CAUTION:

Always turn off the Mic.Check when calibrating the system with an acoustical calibrator. If not

you will add the acoustical and the Mic.Check tone together resulting in a wrong calibration value, often observed
as unstable calibration value.

NOTE:

If the Mic.Check feature is used during a running measurement, the measurement will be influenced by

the inserted voltage signal. Hence, this part of the measurement should be excluded from the results in the post
processing of the measurement data in order to give the correct level on any measured sound source. Please
note that the Mic.Check feature requires the use of the Norsonic Preamplifier Nor1209. All types of measurement
microphones can be used, both polarised and prepolarised. The Mic.Check level is dependant on the microphones
cartridge capacitance. Hence, a ¼” microphone will return a much lower signal level than 90dB. The Mic.Check
feature works also with the Norsonic Dehumidifier Nor1284 and Nor1285 mounted.