Manfred weber M208B Instruction Manual

Instruction Manual

Manfred Weber

Metra Mess- und Frequenztechnik in Radebeul e.K.

Meissner Str. 58 - D-01445 Radebeul

Phone [phone] Fax [phone]

Email: [e-mail] Internet: www.MMF.de

8 Channel

IEPE

Conditioner

M208B

Manfred Weber
Metra Mess- und Frequenztechnik in Radebeul e.K.
Meissner Str. 58
D-01445 Radebeul
Phone [phone]
Fax [phone]
Email [e-mail]
Internet www.MMF.de

Notice: The current version of this document can be downloaded from

http://www.mmf.de/product_literature.htm

Specifications subject to change without prior notice.
© 2009 Manfred Weber Metra Mess- und Frequenztechnik in Radebeul e.K.
No part of this document may be reproduced without the prior written consent of Metra.

May/ 16

Contents

1. Application............................................................................................................4

2. The Instrument at a Glance....................................................................................4

2.1. Connectors and Controls................................................................................4

2.2. Menu Structure...............................................................................................5

3. What is IEPE?........................................................................................................5

4. Description of the Instrument ...............................................................................7

5. Power Supply.........................................................................................................8

6. Inputs and IEPE Supply.........................................................................................9

7. Outputs..................................................................................................................9

8. Grounding and Avoiding Ground Loops .............................................................10

9. Operation ............................................................................................................10

9.1. Gain Selection..............................................................................................10

9.2. IEPE Indicators............................................................................................10

9.3. Overload Indicators......................................................................................10

10. Filters and Integrators........................................................................................11

10.1. Filters .........................................................................................................11

10.2. Integrators..................................................................................................13

10.3. Replacing Filter Modules ..........................................................................15

10.4. Switching Off the High Pass Filters............................................................16

10.5. Switching the IEPE Supply On or Off........................................................17

10.6. Loading Default Settings............................................................................17

11. Calibration.........................................................................................................17

12. Hardware and Software Version ........................................................................18

13. Technical Data...................................................................................................19

Appendix: Warranty

CE Declaration of Conformity

Thank you for using a vibration instrument from Metra!

1. Application

The 8 Channel IEPE Conditioner M208B was designed for piezoelectric accelerom­eters, force transducers, pressure transducers and measuring microphones with IEPE
output. The instrument has the following functions:

• Constant current supply of up to eight sensors

• Gain ranges of 0, 20, 40 and 60 dB

2. The Instrument at a Glance

2.1. Connectors and Controls

4

Figure 1: Front and rear panels

Display

LEDs for gain indication

Overload LED

Constant current LED

Output socket (channel 8)

Input socket (channel 8)

Shared output (channels 1 to 8)

Arrow keys for menu navigation

Escape key for leaving menus

OK key for confirming selections

Key for setup menu

Front Panel:

Rear Panel:

Ground socket

Power supply socket

Reset key

POWER

On/Off switch

2.2. Menu Structure

3. What is IEPE?

The M208B is a signal conditioner for sensors with IEPE output. The abbreviation
stands for Integrated Electronics Piezo Electric and is a common industrial standard
for the output of piezoelectric sensors and microphones. Proprietary brand names,
like ICP®, Isotron®, Deltatron®, Piezotron® etc., are also used for the same purpose.
An electronic circuit inside the sensor transforms the high-impedance signal of the
sensing element into an output signal with low impedance, which can more easily be
transmitted and processed.
A distinctive feature of IEPE is the transmission of supply current and measuring
signal via one single wire, so an IEPE transducer is connected via a coaxial cable.
Figure 2 shows the principle circuit of an IEPE measuring chain. To supply the sen­sor electronics, constant current is used (not to be confused with 4-20 mA current
loops). The constant current is fed into the signal cable by the signal conditioner. A
coupling capacitor keeps the DC components away from the AC signal path.

When constant current is fed into the sensor, a positive DC voltage, called bias volt­age, arises at the sensor terminals. Depending on model and manufacturer, the bias
voltage can be in the range from 5 to 14 V. The bias voltage is modulated with the
measuring signal u

sensor

. The sensor output can never become negative. The minimum
output voltage is approximately 1 V, the saturation voltage of the sensor output
stage. The upper voltage limit is determined by the supply voltage of the constant

5

MENU

1/4: Highpass

2/4: IEPE supply

3/4: Load defaults

4/4: Factory setup

1/2: LED test

2/2: Gain calibration

(password protected)

Figure 2: IEPE principle

Integated electronics

U = 24VDC

I
= 4mA

const

s

Q

U

Sensing element

I

const

Constant supply current

U

s

Supply voltage of constant current source

Coaxial cable

> 100 m

IEPE Sensor

M208B

U

bias

+u

sensor

LED

sensor

indication

Filter

Amplifier

Buffer

Readout unit

0 - 60dB

current source, also called compliance voltage. The M208B uses 24 V. Figure 3
shows the dynamic range of an IEPE transducer.

The M208B features a circuit for sensor check. It can detect the following condi­tions, based on the sensor output voltage:

• No sensor: yellow LED off

• Sensor connected: yellow LED on

The constant current supply can be switched off for each channel (see section 10.5.
on page 17). The sensor detection will then also be deactivated.

6

Figure 3: Dynamic range of IEPE sensors

Max. sensor output =

supply voltage of constant current source

(24 V with M208)

Sensor saturation voltage

(approx. 1 V)

Sensor bias voltage

(see data sheet)

negative overload

0V

positive overload

Sensor dynamic range