MMF M32 User manual

Manfred Weber
Metra Mess- und Frequenztechnik in Radebeul e.K.
D-01445 Radebeul Meißner Str. 58 Internet: www.MMF.de
Tel. [phone] Fax [phone] Email: [e-mail]
Instruction Manual
IEPE Conditioning Module M 2
Application
The IEPE Conditioning Module M32 is a signal conditioner for transducers with IEPE compatible output. It
provides the necessary power supply for the electronic circuit of the sensor. The unit features 3 gain ranges
and a plug in low pass filter. The M32 can be used as a front end for PC based data acquisition systems. It
can be combined with the IEPE Supply Module M28. The M32 is suited for both benchtop applications and
DIN rail attachment in switch cabinets. The wide supply voltage range of the M32 allows power supply from
external batteries, from the available mains plug adapter or from an industrial 24 VDC supply.
What is IEPE?
IEPE is a well established standard for the output of piezoelectric transducers and microphones. It stands for
"Integrated Electronics Piezo Electric". Other brand names for the same principle are ICP®, Isotron®, Delta
tron®, Piezotron® etc. The integrated circuit of the sensor transforms the charge signal of the piezo ceramic
sensing element, with its very high impedance and high EMI sensitivity, into a voltage signal with low im
pedance.
A special feature of the IEPE electronics is that power supply and measuring signal are transmitted via the
same cable. So, an IEPE transducer requires, like a transducer with charge output, only one single ended
shielded cable.
Figure 1 shows the principle circuit diagram. The integrated sensor electronics is supplied with constant cur
rent. This should not be confused with a 4 20 mA current loop. The constant current Iconst is fed into the sig
nal cable of the sensor. A de coupling capacitor keeps DC components away from the signal conditioning
circuit.
The constant current supply and de coupling capacitor are part of the M32.
Figure 1: IEPE principle and functional diagram of the M32
Integral electronics
U = 24VDC
I
= 4mA
const
s
Q U
Piezo ceramics
Iconst constant supply current from M32
UsDC supply voltage of current source in M32
Coaxial cable,
> 100 m
IEPE Transducer M 2
Uoffset
+usensor
LED-
sensor
indicator
G=
1/10/100
Lowpass
module
Amplifier Buffer
Instrument

By supplying the sensor with constant current a positive DC offset voltage arises at the sensor output. This
DC voltage depends on the manufacturer and the specimen and reaches 5 V to 14 V. Round this bias voltage
the measuring signal of the transducer may oscillate. The output voltage of the transducer never changes to
negative values. Its minimum value is the saturation voltage of the integrated electronics (about 1V). The
maximum value of the output voltage is limited by the supply voltage of the constant current source
(24 VDC with the M32). Figure 2 shows the dynamic range of the transducer. The output of the M32 is free
of DC components. It provides the unaltered AC sensor output signal.
Figure 2: Dynamic range of IEPE sensors
Description
The IEPE Conditioning Module M32 (Figure 3) contains the electronic circuit for supplying one sensor. For
multichannel applications additional M28 modules can be plugged into one another by means of screwed in
banana plugs at the side wall of the instrument. These plugs connect the power supply voltage to all modules.
Compatible with the M32:
IEPE Supply Module M28
Figure 3: Functions of the M32
Maximum sensor output voltage =
supply voltage of constant current source
(24 V with M28)
Saturation voltage of sensor,
approx. 1 V
Sensor bias voltage
(see sensor data sheet)
Negative overload
0V
Positive overload
Dynamic range of sensor
Sensor
LED
off
yellow
red
+
-
Power supply
for next module
DIN 45323 socket for
mains plug adapter;
4 mm banana sockets
for power supply by
neigbouring module
Sensor indicator LED
Power supply LED
Input socket
Output socket Gain switch

The M32 requires for operation a supply voltage between 5 and 26 VDC. It can be powered, for example, by:
·Industrial 24 VDC supplies
·The optionally available mains plug adapters PS500 (for one M32) and PS1000 (for up to 3 units M32)
·Batteries with more than 5 VDC
·PC or USB voltage (5 or 12 VDC)
The operating voltage is connected via a circular power connector to DIN 45323 on the left side of the M32.
The tip (inner conductor) is the positive terminal. Alternatively the two banana sockets on the left side of the
case can be used for power supply. Their polarity is shown in Figure 3. A green „Power“ LED indicates the
connected supply voltage.
The M32 is protected against false polarization and line transients up to 60 V. Insulation between power sup
ply and measuring signal is provided.
A supply voltage of 24 VDC for the constant current source is internally generated. This voltage is sufficient
for an optimal dynamic range with all available IEPE compatible transducers. The constant current of the
M28 is approximately 4 mA.
An LED sensor status indicator informs the user of the following conditions: (compare Figure 2):
·LED off: No sensor connected or sensor circuit interrupted.
·LED yellow: Sensor connected properly with bias voltage between 1 and 24 VDC.
·LED red: Input shorted, voltage below 1 VDC.
The gain of the M32 can be selected by a rotary switch between 1, 10 and 100.
The M32 is suited for measurements with piezoelectric transducers from 0.1 Hz to 30 kHz. Thus seismic
measurements at low frequencies with accelerometers or quasi static pressure and force measurements can be
performed. Also shock measurements involving high frequencies and amplitudes are possible with the M32.
The M32 has a replaceable low pass filter module type FB2-... with 4th order Butterworth characteristics.
Metra offers a variety of filter modules with cut off frequencies between 100 Hz and 30 kHz. By unscrew
ing the rear panel and sliding it off the filter module becomes visible (Figure 5). Before replacing the filter,
the power supply must be unplugged. Please make sure that the marking “Pin 1” is in the same position as
the marking on the PCB. The frequency label supplied with the filter module can be attached to the blank
field at the rear panel.
The M32 is well suited for 35 mm DIN rail attachment (Figure 4). For this purpose the adapter M28+32DIN
is available. The adapter base is mounted on the M32 by 2 screws M2.5. Two tapped holes are provided at
the rear of the instrument. As second step the DIN rail bracket is attached by one screw M3.
Figure 5: Replacing the filter module
Note right
position
Figure 4: DIN rail adapter M28+32DIN
Adapter
Screw
M3x3
Screws
M2,5x5
Bracket

Technical Data
Input / output: BNC sockets
Output circuit: DC coupled; impedance approx. 100 W
Dynamic range: ± 10 V
Constant current source: 3.8 .. 5.6 mA, compliance voltage >24 V
IEPE sensor indicator: Bicolor LED; off = open input; yellow = 1 .. 24 V = OK; red = shorted
Gain ranges: 1 / 10 / 100 ± 1 % typically; ± 2 % maximum
Output noise: < 1 mVrms with 30 kHz low pass
Frequency range ( 3 dB): 0.1 Hz .. 30 kHz (depending on lowpass module)
Low pass filter: Plug in module FB2-...; Butterworth; 4th order; attenuation > 70 dB/decade
available frequencies ( 3 dB): FB2 0.1 / 0,3 / 1 / 3 / 5 / 10 / 30 kHz
Power supply: US = 5 .. 26 VDC; < 200 mA; insulated from signal path;
via DIN 45323 circular power connector (positive terminal at tip)
or two banana plugs
Case: Aluminum, connected to negative terminal of power supply
Included accessories: 2 screw in banana plugs for power supply connection with other modules
Optional accessories: PS500: mains plug adapter for 100 .. 240 VAC; 12 VDC / 500 mA
sufficient for one unit M32
PS1000: mains plug adapter for 100 .. 240 VAC; 12 VDC / 1000 mA
sufficient for up to 3 units M32
M28+32DIN: 35 mm DIN rail adapter
Operating temperature: 10 .. 55 ｰC; 95 % relative humidity; no condensation
Weight: 170 g
Dimensions (W x H x D): 56 mm x 59 mm x 44 mm
Warranty
Metra warrants for a period of
24 months
That its products will free from defects in material and
workmanship and shall conform to the specifications
current at the time of shipment. The warranty period
starts with the date of invoice.
The invoice must be presented as proof of purchase.
The warranty period ends after 24 months.
Repairs do not extend the warranty period.
The limited warranty only covers defects which arise as
a result of normal use according to the instruction man
ual.
Metra's obligations under this warranty do not apply in
cases of improper or inadequate maintenance or mod
ification and operation outside the product's specifi
cations
Shipment to Metra will be paid by the customer.
The repaired or replaced product will be sent back to
the customer at Metra's expense.
Declaration of Conformity
According to EMC Directive 2014/30/EC
Product: IEPE Conditioning Module
Type: M32
It is hereby certified that the above mentioned
product complies with the demands pursuant to
the following standards:
DIN EN 61326 1: 2013
DIN EN 61010 1: 2011
DIN 45669 1: 2010
The producer is responsible for this declaration
Metra Mess und Frequenztechnik
in Radebeul e.K.
Meißner Str. 58, D 01445 Radebeul
declared by
Michael Weber
Radebeul, 3rd March 2016
#184 July/08