Note on the instrumentation for measuring electrical proces parameters with electro erosion machining

(1)

Note on the instrumentation for measuring electrical proces

parameters with electro erosion machining

Citation for published version (APA):

Schoot, van der, H. W. P. (1969). Note on the instrumentation for measuring electrical proces parameters with electro erosion machining. (TH Eindhoven. Afd. Werktuigbouwkunde, Laboratorium voor mechanische technologie en werkplaatstechniek : WT rapporten; Vol. WT0216). Technische Hogeschool Eindhoven.

Document status and date: Published: 01/01/1969

Document Version:

Publisher’s PDF, also known as Version of Record (includes final page, issue and volume numbers)

Please check the document version of this publication:

• A submitted manuscript is the version of the article upon submission and before peer-review. There can be important differences between the submitted version and the official published version of record. People interested in the research are advised to contact the author for the final version of the publication, or visit the DOI to the publisher's website.

• The final author version and the galley proof are versions of the publication after peer review.

• The final published version features the final layout of the paper including the volume, issue and page numbers.

Link to publication

General rights

Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain

• You may freely distribute the URL identifying the publication in the public portal.

If the publication is distributed under the terms of Article 25fa of the Dutch Copyright Act, indicated by the “Taverne” license above, please follow below link for the End User Agreement:

www.tue.nl/taverne

Take down policy

If you believe that this document breaches copyright please contact us at:

openaccess@tue.nl

providing details and we will investigate your claim.

(2)

technische hogeschool eindhoven

laboratorlum voor mecl~a~i'~~h;te~hnologie en werkplaatstechniek rapport van de sectie: _{WT-electronika}

titel: Note on the Instrumentation for Measuring Electrical Proces Parameters with Electro 'Erosion Machining.

auteur(s):

H.W.P. van der Schoot

sectieleider: ire S.J. Heuvelman

hoogleraar: prof. dr. P.C. Veenstra sa menvatting

prognose

. ; ~

A description is given of an electronic circuit existing of two differentialamplifiers for

monitoring voltage and current signals and a high speed and-circuit for producing pulses, which are required if voltage and current are both present at the same time.

L-__________________________________ ~1~i---~

biz. van biz.

rapport nr. 02 t 6 codering: P.7.b.12 M.2 trefwoord: !:feten electroerosie datum: juni t 969 aantal biz.

6

+

8

rig. geschikt voor publicatie in:

(3)

Note ,on the Instrumentation for Measuring Electrical Process Parameters with Electro Erosion Machiningj .

.

:

by

H.W.P. van der Schoot

A description is given of an electronic circuit existing of two differential amplifiers for monitoring voltage and current signals and a high speed and -circuit for producing pulses, which are required if voltage and current are both present at the same time.

(4)

HiSh speed count ins 10Sic and monito~ amplifie~s fo~ EDM

The ci~cuit desc~ibed he~e, has been designed fo~ easy measu~ement of voltage and cu~~ent pulses, and fo~ p~oducing pulses, which ~e ~equi~ed

if voltage and cu~~ent a~e both p~esent in the ci~cuit.

Fig. 1 gives the p~inciple of the measu~ement of voltage (U

f) andcu~~ent (if) in the p~ocess.

The voltage is measu~ed ove~ the spa~kgap, while, fo~ meas~ing the cu~~ent,

a small

~esisto~

R h t is mounted in the

ci~cuit

(if

=

~).

. s~ ~.

Because of the complexity of machine~y used one is not f~ee to choose the

ea~thing point of the ci~cuit.

In fig. 1 it is seen that the voltages at points I and 2 a~e U

I

=

Uf + Ui and U2

=

Ui'

So fo~ measu~ing U

i one should use a diffe~ential amplifie~ (Uf

=

U1 - U2).

Fo~ the measu~ment of U

1 one could use an amplifie~ with a single input, but the logic ci~cuit is only sensitive to one pola~ity.

So it is convenient to.use a diffe~ential amplifie~ too, if pola~ity has to be changed.

Fou~ possibilities may occu~ in the ci~cuit:

(1) no voltage and no cu~~ent

(2) voltage and no cu~~ent - spa~kgap too la~ge (3) no voltage and cu~ent - sho~t ci~cuit (4) voitage and cu~~ent.

Only the fou~th case is impo~tant to EDM and should be selected. The numbe~ of times it occu~s should be counted.

Fo~ the selection the logic has been designed.

The demands fo~ a well-wo~king logic a~e amongst othe~s high speed, good sensitivity and sho~t delay.

As fo~ a monitor amplifie~, linea~ity is most impo~tant. The signals may be weak as well as ~athe~ st~ong.

The~efo~e the logic function and the monito~ function were separated to obtain good ~esults.

It is to be noted that the voltage ac~oss the sparkgap may be so high that the signal has to be attenuated; this has been effected by using two 3.9

Kn

~esistors (see fig. 2) which have the advantage that despite the adaptation to 7SQ cables the load over the gap is ve~y small.

(5)

-2-These 3.9 Kn resistors have to be placed as near as possible to the sparkgap to ensure minimu~ capacitive loading.

Note: It is clear that for the current channel 75Q is much more than R h t ' which is of the order of 70 milli-ohms (O.07Q; see report

s un WT 0184).

Fig. 2 gives a block diagram of the amplifier connected to the measuring object.

Note: a and a. - logic amplifiers with differential input for reducing _u 1

the discharge voltage and amplifying the shunt voltage to levels suitable for the logic circuit.

b - high speed and-circuit. c - pulse amplifier.

d and d. - monitor amplifiers (with differential input).

u 1

Some characteristics:

The voltage across the gap can be 10 to 30 volts (burning) and 400V maximum (ignition); so with 3.9 Kn resistors the input voltage will vary from approx. 200 mV to 8V. The shunt resistor for the current measurement is about Rsh

=

70 milli-ohms. The current will vary from

1A up to 100A. So the input voltage will be 100 mV to 10V.

The minimum pulse duration will be 100 ns.

Monitor amplifier

The input signal can be rather high, therefore it is first attenuated by a factor two (R1,2,5 and 6)'

Note: In the circuitdiagram, T1 may be T11 or T₂₁, R1 may be R₁₀₁_{or R201} and so on depending on the part of the circuit.

Then the signal is applied to a differential amplifier with a large controlling area, which is achieved by adding two resistors (R

3 and R4) to the emitter circuit of the transistors T1 and T

2• Further, these two resistors ensure a stable distribution of the current through T1 and T

2, while the sum of currents is kept constant by adding a current source in the common emitter circuit formed by T

3, R10, Zl and R9•

The common mode rejection ratio of the first stage is dependent on this current source and the equality of T1 and T

2• But more important is the attenuater.

So one should choose R1 • R5

=

R2 • R6 within e.g. 0.25%.

(6)

-3-For high frequencies, however, tra~sistorcharacteristics and parasitic capacitors become more important.

As Rl • RS

=

R2 • R

6, also the 3.9 KQ resistors before the voltage input are important to the rejection ratio; R

22, R23 and the equality of Vd of D_l ,2,3 and D4 become significant if high common mode signals are supplied to the input. (See note page 5).

This situation will not be reached because the current channel measures against earth and the voltagechannel gets the current signal (which is 10V max.) as common mode signal after it is attenuated to a signal weaker than 200 mV by the 3.9 Kn resistors in combination with the input impedance. The second amplifier stage is single ended and is followed by an emitter-follower with an output impedance of approx. 7SQ.

This stage is shortcircuitproof during short times.

The DC level of the monitoroutput can be made zero by slightly changing R

13• A higher value of R13 will force the output to the negative and a lower value to the positi.ve side.

Counting logic

Both channels start with a Fairchild ~A710 high speed differential comparator.

The input is protected to high input signals with four high speed diodes and two resistors (R

22 and R23, Dl to D4). See page 5.

To prevent noise and other interfering signals from giving an output, the comparator is forced to negative output by means of R₂₄, which is connected from the non-inverting input to the -6V supply.

This also includes that weak signals will not give an output (see technical data) •

The comparators are followed by a gate (D_1S' D_2S' R₃₀₁_{,302 and R303 ) an} inverter (T

31) and a threshold formed by D31, R30S and R306 (see fig. 3); this combination is called "b" in fig. 2.

The threshold improves the noise immunity and the speed of the counting logic. The last stage is an emitterfollower like that of the monitor amplifiers.

The output has a positive DC level and the output pulses are of negative polarity.

Note: As mentioned at "monitor amplifier" it is important to choose in the voltagechannel the 3.9 KQ resistors. and R

20 and R21 equal to each other within e.g. 0.2S% and R22

=

R

23 within 2% to obtain a good rejection-ratio.

(7)

-4-When building these circuits one should mount the input and the output plugs isolated from each other to prevent parasitic earthcurrents. The figures 3, 4 and 5 represent: circuitdiagram, list of components and printed circuit board with component location.

Technical data

Monitor amplifier

Attentuation, loaded with 750 cable approx. 1.5 meters long, terminated with 750: 5x.

Bandwi~t~3dB: 12 MHz.

Delaytime for several input voltages: leading·edge 20 rear edge 20 ns Rise time: 20 ns

Fall time: 20 ns

Maximum input voltage for linear operation: 10V (peak) Common mode rejectionratio: at 1 MHz: 300

Counting logic

at 2.5 MHz: 150 at 5 MHz: 100 at 7.5 MHz: 80 at 10 MHz: 70

Balanced input: input impedance 2x 750 Output impedance: 750

DC level of output (loaded with 750): + 3V Maximum input voltage: 10V

Output pulse (output loaded with 78~ro: 3V Rise time: 20 ns

Fall time: 20 ns

Delay times measured with a 100 ns input pulse:

ns

input pulse O.lV to lV: leading edge 70 ns to 20 ns. rear edge 40 ns to 90 ns. input pulse 1V to 10V: leading edge 20 ns.

rear edge 90 ns.

Minimum input pulse (100 ns) to obtain an output pulse of full amplitude: 75 mV (delay time approx. 100 ns).

Minimum input signals (sinusoidal) to obtain an output pulse:

at1 MHz 50 mV ,at 5 MHz 70 mV and at 10 MHz 150 mV

rIDS rms rms

Output signal if no pulse has to appear: Less than 10 mV p_p'

(8)

-5-Power supply

Fig. 6 represents the ciI'cuitdiagI'am of the power supply which is rather simple but well functioning.

A part of the output voltage is compared with the reference

Z2

by means of T

4, which controls the boosteI'T2 of the poweI'tI'ansistoI' Ti .

To change the output voltage, the value of RS or R7 can be changed. A smaller value for RS or a higher value for R7 gives a lower output voltage. A higher value for RS or a smaller value for R7 gives a higher output VOltage.

For final alignment of the logic it would be convenient to make sure first that the power supply voltages are within some per cent of the indicated values.

A simple current limit has been realised with T

3, R3 and R4• The circuits for +12V and -12V are identical.

The figures 6,7 and 8 represent: ciI'cuitdiagI'am, list of components and printed circuit board with component location.

Technical data

Output voltages: +12V and -12V. Current limiting at 0.65A.

Line regulation: + or -10% line voltage change will give output changes less than 1 mV (measured with a 10adcuI'I'ent of 250 rnA).

Load regulation (DC): a current change of 0.2A gives an output change of less than 12 mY.

Noise and ripple: Less than 15 mV peak to peak.

~: As mentioned in chapter "Counting logic" the only function of Dl1

to D14 and D21 to D24 id to protect the microcircuits to high voltages. If high common mode signals (>V

D) are applied to the inputs an outputsignal may occur, because of the diff~rent diode voltages (e.g. V_D12 > V_D13 or

V_D14 > V_Dll)·

Replacing D₁₃, D₂₃, Dll and D21 by two diodes (same type) will prevent this situation.

This modification does not change the measuring capabilities of the

circuit, since there will be no output in case where the common mode signal is higher than V

D, even when the noninverting input (n.i.) is positive with respect to the inverting input.

(9)

~ __ -r~~Ir---,!;;---t.:I~--

--a

~ ____ ~ ______ ~t

,r--- - - - -- -- - -

- - I 1

I I . , . .

losciUosc.op8

I

_UFrrto"ito,.;I\'

'-

-I

I I I COUNTE/( I I I

. I

\

>---41'

O.sdU.oSCOpE I

tf __

,.ilo,.;~

...

_---

- _I

(10)

+tlv .(3) IU.

-,,,

. etl

I. +tll' ~.---~ D

-4"

o

~

_(i

c",

Note: nUMlthe"s oe.i...,ee" C) ~;a;,.i;e t:J..e. eoltlte~e.lOHs

Oh t:l.e P.c.h_,..J. (,c;:J.$) -ltv

....

(#) +Iltl C~) 0

(11)

[IJ.'I

L/st

tIl

COM,.t!lIfI!If'S (Ctwlle,itJLDJ'C).

'R1t1I

'RUI ~"9

~ 1111 Ibot ~ 120

'R ,oJ _1tus

'An.,

'tfl'¥ Ilt~

6eon. 1h.u

"A f'~ itlOS' ~".u

'R

,,,t

_Itt,,' _'Rllt

RII, 1l :tOil 1l3",

R'll'

Rlol Riot

RIll Riot fkD.. ftaD3

1>. lID ?lllO liDn. ~30t

Ii ,,, _lU" _,-sIcA _1hD5

1\111. 1\111 Ulctl. 1h."

Rm ~IIJ 100.0.. ~Jo1

~'1t' Ru¥ 1aJdl 1lJoI

AUr 1hls lOA 'RJ",

'A/I/' 1tU& "OA ~j'o

1(11; 1h,? fOA 1.111 R118

Ru,

,SA 1;,

~}

111

'Ii! 135)'39

1fJ

lis

"lit

1;'1

_?it

1;,. _~,.

_fit

~, Z>u V,! D.zt Z>,J Dtl 1)/1,( D21f 'D,s-

DeS'

1>Jf

z"

Zi,

Z.3f I1PS'~t'I

HIt1/!!

(witJ

to.t,iI.1"';)

ffl91Ji

ZCII~r"'iDJIl ,,/I

'2ber"'''o''~

'"

fl!', 1fnO 1hl1 1l.tU RUI

'121.

,,"A

ALL ,-.,iston,

18

W.41 &lcCf,t:

II1.rt. "AWl J R .. , j

!IIV'

~.ct. ;i?'o9, "3ft

"IV

IkA

.fico. : 1;

"It_llf

~d'

reJectlolf

rtJ/.·hti'S

/J.okn. fDr tl." Mil"';'." 4"'!'l,!ie,.. Dlle

fJeLL

si ... ,,,,

e/."osc:

"1D_.tl. 71'1;7 ·~1"":: 'lft!l~ .Rftll fDfJ..Q. ~~D7·'lllo$'

=

lib" .7(&~

lien. l.lleA ~ •. 2Jca fDA fkn. f1'on.

J5.a..

!;OA

(12)

{!tI

p,.;"teJ

e/I"tu.""

Boo,."

•

....

,

'

...

Hole.

Nflte /~ s/'DrlCi're,...l/;Aj

bQIA

siDles .

of

/c

~OQrI ////;00'«2 /

('?I'Il,.

'~U'

(13)

I I s,

I.-'-'-'---'-'-'-'-'-'---'-'_.!

I I

I

I I

I

I ...

...--..,..;....:;C)--.I

I--"-'=:-~I----"'"

Sa (1)1

s,

(J)I

I .

I

i

I I

~~;..,;o.-.I

I , ___

-.=----=b---.

I

r

I

· ~/I."

I

· I

·

~,) 1'-...

--+---...

- - 0 0 0 I

. I I·

I

titlJpF

I

J\

I

w

.

... --, I

:

tIl

I

:1, (&}.

I

Sif ( • I

r

~

I I

!

I

~-

_()/I

-I

J •

I I.

Sa (.

I

Sh/ll-s~"""""o~=--L-.

_. _ . _. _. _. _ .'_. _. _. _

.. _ . _.

--l

~/%V

-?T.

power

Supplr

~" /lffl'l Fw/. 61)D

(I'IAlJ",.,.)

.

",,,

e~,.,t .E[

18/'1..6

f,-I'"

s,-s"

5J-S

t SS'-

5,

'1 -Sa

.2.1. I) r/ "" /'-$'[/..., • /1.$'/...,

/I.rv'y

/'.st/~

S4,

SJ/e'" / .

6:J.II,,~4'e,/ -4i11

AJlel'4L

~t:t,e

51,

t.

$,I;6l"

I.

~,,.,,

,el,,"

if,

"S&~l

elVll.·

c:" Z I'

"'!J

lIumie,.,s

ieiwee" ()

;ntJI,;~4/e

tie

cl)"",eetIQlfs

(14)

h.,.,

".,1

o(

eO"'fMeIf~$ ("t>fIII~"

S",.",?,)

~" 1l.t1

f.1Jdl.

Y-t-.."

~n ~12 !,IDA.

f,w

1l1J llt~ f()O A

'1,w

~'t 'RI.'I

f.n.

%w

'Ii"s- "lias- 5'6D..IJ.

few

11" ~2~ 3.3kD.

few

lI,jZ ~11

6,uJcfJ.

Yew

"'9

nt'

~.9kn.

z,JtI

en

41

H~ -tDV

eft (1.1.

lS;;:;

_3DJ!

t:1J C1.J

11/

wY

7;

_lit

Pl3U'~ f.tJ1--J1. lDiiI.,,.. Jl/A lSY .. 9

Scltal/"'"

f.:r.

~.t Beft>";

1iJ

1.iJ &ftJ'1

1i"

?it ~1()' ,

Zft _Ztf 21l".t,,:1/,,"'~ jrV

Z'Z z,~ ZeAe,.JlH!c

7 Y

~f

_2!J

~)( flY9f¥

(15)

(fl1.V) 9 (orl-) 10 (-I~v) 1f

-•

• .

-... '''''., .. ---,;,_ .. '"'''''.,,. ,,'~,,--~. "'"',-... ".- • ~."~._. _ _ _ _ _ _ _ _ _ _ . , , . _ - . , · · " .. < ___ ,,.,., _ _ ' .. " . _ . . ... wn ... ,._ ' ... _

•

I

•

GO

• ..

c e 1;.,

..

_1"

- -

• ..

. b

e

h

e

c Co

C,"

C

!l

-

"

• .-Ca.\--

--",--

.-e,,--

·-R,t--

\

R"

.-1t11- _.~.

• -R,,-

1':.

I

. -

.

-

.

-,1J'l:

_•

sf:

:"'''.

e _, C

-~-

-,

• .,c

_.-Rt'-.

..

~

--It'l-_

It""

_{/ t}

.

,-(zu

j

·-'Ru-

_{CZ, ..}

":J 6

--!f,,--• _{U_8/,,!}

_\

.

"'::C11;:--.t;/

,&.

• Cz,;:>

.

_•

C!z,,::l _l. _{&. """}

-rl,

/ t

<:."

I

.... R,,-.

.-R1S'-·

• I

--1./$--J,

--11'1- A.-...:~_"t • •

1ft"

~.

R

1'1

.1' ..

"?...

\

• -::C,.-" c " 0. •

t •

_I.e

1 I .,

_.c + 'C J. ., "

"

,

.

.,

..

:

.

,

..

_...

.

I

_,

f

-y.:;!J.8

?,./ntetl

e,"'I!/4/-l

B

D«,.,/ .~ it t 1 9 8

(16)