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Instruction Manual

Manfred Weber

Metra Mess- und Frequenztechnik in Radebeul e.K.

Meissner Str. 58 - D-!""5 Radebeul

#hone $"%-&5!-8&' (!%! Fa) $"%-&5!-8&' (%"

*+ail, InfoMMF.de Internet, .MMF.de

Charge

Amplifiers

M68 Series

mailto:Info@MMF.dehttp://www.mmf.de/http://www.mmf.de/mailto:Info@MMF.de

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The latest version of this document can be downloaded from:

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

Manfred Weber

Metra Mess- und Frequentechni! in "adebeul e.#.

$u%. &' (&)*

http://www.mmf.de/produktliteratur.htmhttp://www.mmf.de/produktliteratur.htm

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Contents&.$pplication................................................................................................................................+

*.Function and ,peration.............................................................................................................+

.ower uppl0............................................................................................................................ )

.&.1roundin% 2oncept............................................................................................................)

.*.34ternal uppl0 .................................................................................................................)

..5atter0 ,peration 6M)78&9...............................................................................................

;.ow ass Filter .......................................................................................................................&&

=.?i%h ass Filter....................................................................................................................... &*

&'.imited Warrant08eclaration of 2onformit0

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Fi%ure &: Front view of Model M)78& with control elements

;

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1. Application

The i%nal 2onditioners of M)7 series are intended for connection of pieoelectric acceleration@

force or pressure transducers. The input is suitable for sensors with char%e output as well as for

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bandwidth down to '.& ? comes into effect. The filters are followed b0 the second amplifier

sta%e. The divided %ain before and after filterin% provides sufficient d0namic ran%e@ even for si-

%nal components outside the filter ran%e. $t the same time a hi%h si%nal-to-noise ratio is achie-

ved.

5efore reachin% the output driver the si%nal ma0 pass one or two inte%ratin% sta%es. The output

is 82 coupled.$ control >38 for the output modulation indicates an output si%nal hi%her than + G of full-scale

modulation. $n overload >38 shows if the output si%nal e4ceeds =' G of full-scale modulation.

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The suppl0 volta%e is connected to the terminals EI + .. &+ HE and E' HA. $ special plu% with

screwed contacts for the rear soc!et is delivered to%ether with the instrument. This wa0 the

power suppl0 can be wired manuall0.

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$ peculiarit0 of

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Fi%ure +: 80namic ran%e of

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$ star-shaped %roundin% networ! is the ideal solution to avoid %round loops. tar-shaped means

that all %roundin% wires of the sensors and the amplifier outputs are tied to %round at the si%nal

conditioners@ without an0 transverse connections. 38s indicate minimum modulation and overload condition.The >38 E+GA li%hts up at an output volta%e hi%her than '. H. The >38 E,H>A li%hts up ifthe output volta%e e4ceeds = H.

The optimum %ain ran%e is selected@ if the >38 E+GA li%hts up and the >38 E,H>A remains

dar!. 38s remain dar!@ the %ain should be increased. 38s li%ht up the %ain

should be reduced.

The overload detector monitors both the amplifier output and the filter input 6see Fi%ure *9. 50

that means overload condition will also be indicated when hi%h si%nal components be0ond the

filter pass band occur.

$n overload detector at the inte%rator input is not provided. 38 indicates overload 0ou can use the low pass filter to attenuate hi%h frequencies.

&'

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8. o Pass FilterTo eliminate disturbin% noise or to compl0 with the hannon theorem: Ei%nal frequenc0 shouldbe less than half of the samplin% frequenc0A@ it can be advanta%eous@ to use a low pass filter. Forhi%her accurac0 in the time domain it is recommended to set the low pass at &/&' the samplin%frequenc0.

The instruments of M)7 series have ) internal low pass filters. The scale at the positions of thefilter switch E>,W $A is shows the d5 limitin% frequencies in !?. The followin% table

shows the d5 and the &' G limitin% frequencies of the low pass filters:

3 dB Frequency

&'' ?

'' ?

& !?

&' !?

*' !?

+' !?

10 % Frequency

' ?

*'' ?

'' ?

!?

&; !?

+ !?

The slope of the low pass filters is ;' d5 per decade.

&&

!8C

-!8C

-%C

%C

B! ! ! !k9z

dD

-( dD

-" dD

B! ! ! !k9z

! k9z

! k9z

! k9z

! k9z ( k9z

5 k9z

( k9z

5 k9z

Fi%ure ): T0pical frequenc0 and phase response of the low pass filters

!8C

-!8C

-%C

%C

dD

-( dD

-" dD

! ! ! !9z

! ! ! !9z

! 9z

& 9z! 9z

& 9z

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0. igh Pass FilterThe M)7 si%nal conditioners have a hi%h pass filter with a lower limitin% frequenc0 of ? 6-

d59. 50 means of this filter low frequenc0 noise can be removed. >ow frequenc0 noise ma0

occur@ for e4ample@ b0 the influence of temperature transients to pieoelectric compression t0pe

accelerometers. The slope of the ? hi%h pass filter is ;' d5 / frequenc0 decade. The ?

hi%h-pass filter is switched on b0 turnin% the E

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Vibration acceleration a6without inte%ration9:

a=uout

GBua

6a in m/sOP uoutin mHP 1 in mH/mHP 5uain mH/ms-*9

Vibration velocity v6sin%le inte%ration9:

v=uout

GBua

&'

6v in mm/sP uoutin mHP 1 in mH/mHP 5uain mH/ms-*9

Vibration displacement d 6double inte%ration9:

d=uout

GBua

&''

6d in QmP uoutin mHP 1 in mH/mHP 5uain mH/ms-*9

The equations above appl0 for

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38 remains dar!.

This can occur due to the attenuation of hi%her frequencies b0 the inte%rator 6compare Fi%ure 79.To avoid possible overload@ ma!e sure to chec! the si%nal level in the switch position E$22A

6inte%rator off9 before usin% the inte%rator.

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11. ac4 Cases for Model M681For the &=A unit M)7"& the followin% rac! mountin% cases are available:

Model

M)75)

M)75&*

Channels

)

&*

Built-in poer supply

0es

0es

The rac! cases Models M)75) and M)75&* suppl0 the plu%%ed-in modules via a bac!plane.

The0 can be operated with both &&+ H$2 and *' H$2 without chan%in% an0 settin%s.

&+

Fi%ure &': Front view of rac! case M)75&*

Fi%ure &&: "ear view of rac! case Model M)75)

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$ternal supply + .. &+ H82

V '' m$ 6M)78&@ M)7"&9V & $ 6M)789connector to 8

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'imited 4arranty

Metra warrants for a period of

5 months

that its products will be free from defects in material or wor!manship

and shall conform to the specifications current at the time of shipment.

The warrant0 period starts with the date of invoice.

The customer must provide the dated bill of sale as evidence.

The warrant0 period ends after *; months.

"epairs do not e4tend the warrant0 period.

This limited warrant0 covers onl0 defects which arise as a result

of normal use accordin% to the instruction manual.

MetraRs responsibilit0 under this warrant0 does not appl0 to an0

improper or inadequate maintenance or modification

and operation outside the productRs specifications.

hipment to Metra will be paid b0 the customer.

The repaired or replaced product will be sent bac! at MetraRs e4pense.

&7

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&=

,eclaration o( Con(ormity

roducts: 2har%e $mplifiers

Models: M)78&@ M)78@ M)7"&@ M)75)@ M)75&*