MegaSig MPA668-812 User manual

Equips engineers to create better products
Page 1 of 6
Shenzhen MegaSig Co.,Ltd www.megasig.com Tel: [phone] / Fax: [phone]
Instruction manual for free-field
measurement microphone kit
MegaSig Measurement & Control Technology Co.,Ltd

Equips engineers to create better products
Page 2 of 6
Shenzhen MegaSig Co.,Ltd www.megasig.com Tel: [phone] / Fax: [phone]
1、Product introduction
1) Type and designation：MPA668-812 Free-field measurement microphone kit
2) The model code of the free-field measurement transmission kit is as
follows:
MP A 668-812
Stands for "Specific model of preamplifier"
Stands for "Specific model of microphone"
Stands for "Preamplifier"
Stands for "Microphone"
3) Explosion-proof marks：Ex ic IIB T4 Gc
4) Execution standard：GB/T 3836.1-2021 、GB/T 3836.4-2021 、
IEC 60079-0:2017、IEC 60079-11:2011
5) Feature：The free-field measurement microphone kit is an explosion-proof
certified special microphone kit，In line with the dangerous area 2 zone
and explosive environment IIA, IIB class T1-T4 temperature group use
requirements, can ensure the use of safety in dangerous gas environment;
It is composed of microphone MP 668 and preamplifier MA 812 (Figure
1.1). The microphone and preamplifier are connected with threads.
Figure 1.1
MP 668
MA 812

Equips engineers to create better products
Page 3 of 6
Shenzhen MegaSig Co.,Ltd www.megasig.com Tel: [phone] / Fax: [phone]
Among them, MP 668 is a 1/2 inch pre-polarized free field
measurement microphone (Figure. 1.2), which is used to measure the true
sound pressure without distortion before the sound field is inserted. The MP
668 body is made of stainless steel, giving it good toughness and long shelf
life.
Figure 1.2
Please be careful when using：Microphone diaphragm is extremely
fragile, do not touch the microphone diaphragm with hands, do not easily
remove the guard bar, so as not to cause damage to the microphone.
The MA 812 preamplifier (Figure 1.3) is a preamplifier powered by a
constant current source，It has high input impedance, low background noise
and wide frequency response range. The output interface adopts BNC joint,
and the main part is made of stainless steel to make it have good toughness
and long time storage.
Figure 1.3
Protection grid
Diaphragm
Threaded connections
BNC Connector

Equips engineers to create better products
Page 4 of 6
Shenzhen MegaSig Co.,Ltd www.megasig.com Tel: [phone] / Fax: [phone]
2、Specifications
Field Free-field
Frequency range （dB）6.3Hz-20kHz±2dB 12.5Hz-10kHz±1dB
Dynamic range （dB）17dB-146dB(1000Hz THD<3%)
Sensitivity mV/Pa(dBV/Pa) 44.5mV(-27dB)±2dB
Polarization voltage 0V( Prepolarized )
Power supply 4mA
Typical capacitance 16.0pF
Connector BNC
Temperature range -20℃~60℃
Humidity range non condensing 10%-90%
Overall length 85mm
Diameters 13.2mm
Diameters（No Protection grid） 12.7mm
Cooperate with thread 11.7mm-60UNS
3、The product principle
Internal structure drawing of microphone：

Equips engineers to create better products
Page 5 of 6
Shenzhen MegaSig Co.,Ltd www.megasig.com Tel: [phone] / Fax: [phone]
Using a special process will charge into the microphone electret
material on the back plate(Electret materials are used to keep the charge of
the injection in place), Thus a capacitor is formed between the back plate
and the diaphragmWhen the sound in the environment drives the
diaphragm to vibrate, the vibration changes the distance between the
diaphragm and the back plate, thus changing the charge of the capacitor.
After the signal output from the microphone is amplified by the
preamplifier, we can use the data acquisition card to collect the signal of
sound change.
Schematic diagram of preamplifier circuit:
4、Method of use
1）、The microphone uses BNC coaxial cable (i.e. power supply and
signal output share one cable), Supply 4mA constant current power supply,
working voltage is 24V DC. Can work normally.
2）、Intrinsic safety parameter：Ui：24VDC，Ii：10mA。

Equips engineers to create better products
Page 6 of 6
Shenzhen MegaSig Co.,Ltd www.megasig.com Tel: [phone] / Fax: [phone]
5、Precautions for Use
1）Do not hot swap
2）Operate the microphone carefully and keep the diaphragm away from
dust and other objects
3）Do not touch microphone diaphragm with your hands
4）It is recommended not to remove the microphone protection fence at
will
Version Document number Date Design Verify Approve
V1.1 MGS-MP668-01 2022.08.09 Tianyang Jiang Kanghui Zhao Xushun Chen