Instruction manual M28

Instruction manual M28
Manfred Weber
Metra Mess- und Frequenztechnik in Radebeul e.K.
D-01445 Radebeul
Meißner Str. 58
Tel. +49-351-836 2191 Fax +49-351-836 2940 Email: [email protected]
Instruction Manual
IEPE Supply Module M28
The IEPE Supply Module M28 is designed to connect piezoelectric sensors to measuring instruments or data
acquisition systems which do not have IEPE compatible inputs. It supplies the power for the sensor electro nics and de-couples DC components from the sensor signal. The M28 can be combined with the IEPE Conditioning Module M32 featuring additionally selectable gain and low pass filtering. The M28 is suited for
both benchtop applications and DIN rail attachment in switch cabinets. The wide supply voltage range of the
M28 allows power supply from external batteries, from a mains plug adapter or from an industrial 24 VDC
Figure 1 shows the principle circuit diagram. The integrated sensor electronics is supplied with constant current. This should not be confused with a 4-20 mA current loop. The constant current I const is fed into the signal cable of the sensor. A de-coupling capacitor C c keeps DC components away from the input of the connected instrument.
Providing the constant current supply and de-coupling the output is the purpose of the IEPE Supply Module
IEPE Compatible Transducer
Us = 24VDC
Built-in electronics
= 4mA
Coaxial cable
CC=10 µF
> 100 m
+u sensor
Piezo ceramics
R O=220k
Coupling capacitor of the M28
Iconst Constant current of the M28
Input resistance of the instrument
Output resistance of the M28
Supply voltage of the constant current source of the M28
Figure 1: IEPE principle and functional diagram of the M28
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®, Deltatron®, Piezotron® etc. 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 trans ducer 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 M28). Figure 2 shows the dynamic range of the transducer. The output of
the M28 is free of DC components. It provides the unaltered AC sensor output signal.
Positive overload
Sensor bias voltage
(see sensor data sheet)
Saturation voltage of sensor,
approx. 1 V
Dynamic range of sensor
Maximum sensor output voltage =
supply voltage of constant current source
(24 V with M28)
Negative overload
Figure 2: Dynamic range of IEPE sensors
The IEPE Supply Module M28 (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 ba nana plugs at the side wall of the instrument. These plugs connect the power supply voltage to all modules.
Input socket (BNC)
Sensor indicator LED
DIN 45323 power supply
connector /
banana socket to next module
Power supply
for next module
Power suply indicator LED
Output socket (BNC)
Figure 3: Functions of the M28
Compatible with the M28:
IEPE Conditioning Module
M32 with selectable gain and
plug-in low pass filter
The M28 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 up to 3 M28) and PS1000 (for up to 6 M28)
• 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 M28.
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 M28 is protected against false polarization and line transients up to 60 V. Insulation between power supply and measuring signal is provided.
Internally a supply voltage of 24 VDC for the constant current source is 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 M28 is suited for applications with piezoelectric transducers over a frequency range from 0.1 Hz to
100 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 M28.
To reach the lower frequency limit of 0.1 Hz (-3 dB) the input resistance of the instrument connected to the
output of the M28 must not be lower than 1 MΩ. At 100 kΩ input resistance the lower frequency limit will
increase to approximately 0.3 Hz.
The M28 is well suited for 35 mm DIN rail attachment. For this purpose the adapter M28+32DIN is available as shown in Figure 4. The adapter base is mounted on the M28 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.
Screws M2,5x5
Adapter Base
Screw M3x3
DIN Rail Bracket
Figure 4: DIN Rail Adapter M28+32DIN
Technical Data
Input / Output:
BNC sockets
Output circuit:
AC coupled over 10 µF; 220 kΩ parallel with output
Load resistance > 1 MΩ for lower frequency limit 0.1 Hz (-3 dB)
Dynamic range:
up to ± 10 V (depending on sensor type)
Constant current source:
3.8 .. 5.6 mA, compliance voltage >24 V
IEPE sensor status indicator:
bi-color LED; off = input open; yellow = 1 .. 24 V = OK; red = shorted
Gain / Accuracy:
1 ± 0,5 %
Output noise:
< 1 µVrms (2 Hz .. 24 kHz)
Frequency range (- 3 dB):
0.1 Hz .. 100 kHz
Power supply:
US = 5 .. 26 VDC; < 100 mA; insulated from signal path;
via DIN 45323 circular power connector (positive terminal at tip)
or two banana plugs
Aluminum, connected with negative supply terminal
Supplied accessories:
2 screw-in banana plugs for power supply connection with other modules
Optional accessories:
Operating temperature range:
-10 .. 55 °C; 95 % relative humidity; no condensation
120 g
Dimensions (W x H x D):
33 mm x 59 mm x 44 mm
mains plug adapter for 100 .. 240 VAC; 12 VDC / 500 mA
sufficient for up to 3 units M28
mains plug adapter for 100 .. 240 VAC; 12 VDC / 1000 mA
sufficient for up to 6 units M28
M28+32DIN: 35 mm DIN rail adapter
Limited Warranty
Metra warrants for a period of
24 months
that its products will be free from defects in material
or workmanship and shall conform to the
specifications current at the time of shipment.
The warranty period starts with the date of invoice.
The customer must provide the dated bill of sale
as evidence.
The warranty period ends after 24 months.
Repairs do not extend the warranty period.
This limited warranty covers only defects which arise
as a result of normal use according to the
instruction manual.
Metra’s responsibility under this warranty does not apply
to any improper or inadequate maintenance or modification and operation outside the product’s specifications.
Shipment to Metra will be paid by the customer.
The repaired or replaced product will be sent back
at Metra’s expense.
Declaration of Conformity
Product: IEPE Supply Module
Model: M28
It is hereby certified that the above mentioned
product complies with the demands
pursuant to the following standards:
EN 50081-1
EN 50082-1
Responsible for this declaration is the producer
Metra Mess- und Frequenztechnik in Radebeul e.K.
Meißner Str. 58
D-01445 Radebeul
Declared by
Manfred Weber
Radebeul, 2nd of July, 1999
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