senso s
A icle
Cha ac e iza ion and Di e en ia ion be ween Oli e
Va ie ies h ough Elec ical Impedance Spec oscopy,
Neu al Ne wo ks and IoT
JoséMiguel Madueño Luna 1,* , An onio Madueño Luna 2
and Ra ael E. Hidalgo Fe nández 3
1G aphics Enginee ing Depa men , Uni e si y o Se ille, 41013 Se ille, Spain
2Ae ospace Enginee ing and Fluid Mechanical Depa men , Uni e si y o Se ille, 41013 Se ille, Spain;
[email p o ec ed]
3G aphics Enginee ing and Geoma ics Depa men , Uni e si y o Có doba, 14014 Có doba, Spain;
[email p o ec ed]
*Co espondence: [email p o ec ed]
Recei ed: 20 Sep embe 2020; Accep ed: 16 Oc obe 2020; Published: 20 Oc obe 2020


Abs ac :
Elec ical impedance has shown i sel o be use ul in measu ing he p ope ies and
cha ac e is ics o ag i- ood p oduc s: ui quali y, mois u e con en , he ge mina ion capaci y in seeds
o he os - esis ance o ui . In he case o oli es, i has been used o de e mine a con en and
op imal ha es ime. In his pape , a sys em based on he Sys em on Chip (SoC) AD5933 unning a
1024-poin disc e e Fou ie ans o m (DFT) o e u n he impedance alue as a magni ude and phase
and which, wo king oge he wi h wo ADG706 analog mul iplexe s and an ex e nal p og ammable
clock based on a syn hesized DDS in a FPGA XC3S250E-4VQG100C, allows o he impedance
measu emen in ag i- ood p oduc s wi h a equency sweep om 1 Hz o 100 kHz.
This pape
demons a es how elec ical impedance is a ec ed by he empe a u e bo h in eshly picked oli es
and in hose p ocessed in b ine and p o ides a way o cha ac e ize cul i a s by making use o only he
elec ical impedance, neu al ne wo ks (NN) and he In e ne o Things (IoT), allowing in o ma ion o
be collec ed om he oli e samples analyzed bo h on a ms and in ac o ies.
Keywo ds:
elec ical impedance; SoC AD5933; a i icial neu al ne wo ks (ANNs); in e ne o hings
(IoT); empe a u e
1. In oduc ion
1.1. The E ec o Tempe a u e
Tempe a u e a ec s he ex u e o ui and ege ables, bo h aw [
1
] and cooked [
2
], and i also
a ec s hei elec ical pa ame e s such as he elec ical impedance o hei pulp. A wide a ie y o
p ocedu es and equipmen [
3
,
4
] exis o ob ain a ious pa ame e s associa ed wi h he pulp o hese
ui s and ege ables (pene a ion esis ance, iscosi y, e c.)
In he case o oli es, he e a e no s udies explici ly analyzing he in luence o empe a u e on
he ui , especially in i s elec ical pa ame e s, al hough i s e ec is known in ce ain mechanized
oli e p ocessing p ocedu es. This is he case, o example, in he indus ial oli e pi ing p ocess [
5
],
which is done by au oma ic machines whe e clamps a e used o ap he oli e, while a punch needle
goes h ough he clamps and, consequen ly, he oli es, causing hem o be de-s oned. This ype o
machine eaches a conside able pi ing speed, which ob iously means a minimum cos pe uni o ui
de-s oned. Howe e , he e y clamps ha hold he ui in place and he de-s oning ool cause b eakage
in a conside able numbe o oli es du ing no mal ope a ion, which can be o he o de o 14%, especially
Senso s 2020,20, 5932; doi:10.3390/s20205932 www.mdpi.com/jou nal/senso s
Senso s 2020,20, 5932 2 o 20
in he “Go dal Se illana” oli e a ie y. While he p oduc i i y o hese pi ing machines makes hem
mo e cos -e ec i e despi e he pe cen age o oli e b eakage compa ed o p e ious de-s oning sys ems,
hese machines p esen a se ious p oblem, as he pe cen age o b oken oli es is qui e conside able.
While mechanical solu ions educing he pe cen age o oli e b eakage in such de-s oning machines
do no exis , i has been p o en ha cooling he oli es p io o pi ing minimizes he p oblem o he
poin ha , wi h adequa e e ige a ion, he pe cen age o b oken oli es du ing he pi ing p ocess is o
he o de o 2%, o he “Go dal Se illana” oli e a ie y p e iously ci ed.
Fu he mo e, he cu en consume end o lowe sal and acidi y [
6
] means ha a signi ican
p opo ion o he oli es de e io a e du ing he ime hey spend in e men e s. A e a ew mon hs a an
a e age empe a u e o 25
◦
C, he p obabili ies o ha ing a signi ican loss o p oduc in he pi ing
p ocess a e e y high, due o a loss in i mness in he oli es, especially he la ge ones, which a e he
mos in demand on he ma ke . By cooling o empe a u es close o 7
◦
C (in some cases i eaches
0◦C
,
depending on he cooling sys em and he cos s he company wan s o ake on in he p ocess), i is
possible o inc ease he i mness o he oli es while main aining all o hei cha ac e is ics, he eby
educing he loss o p oduc due o he oli es ha ing a mo e igid ex u e. In addi ion, his cu s down
on he hou s he machine is wo king, meaning a dec ease in machine jams and hou s when he punch
needles a e s opped.
One way o cha ac e izing he s a e o he oli es p io o de-s oning would be by doing an
elec ical impedance measu emen on a ep esen a i e sample. As will be demons a ed in his s udy,
he elec ical
impedance o he oli e pulp is no only a ec ed by he oli e a ie y o he ype o
indus ial p ocessing (g een “Se illana S yle” o black “Cali o nian S yle” oli es) [
7
], bu also by he
empe a u e. Fo his eason, cha ac e izing his elec ical pa ame e e sus he empe a u e (especially
be ween 7
◦
C and 0
◦
C) o a gi en ype o indus ial p ocessing would show whe he o no oli es a e
ap be o e pi ing.
1.2. Elec ical Impedance: Measu emen
The de e mina ion o elec ical p ope ies is used in a wide ange o disciplines and indus ies [
8
].
In he ag i- ood sec o , he use o elec ical conduc i i y is applied o he de e mina ion o di e se
cha ac e is ics in ag i- ood p oduc s [
9
,
10
] such as os sensi i i y, eezing ole ance, mois u e con en ,
and seed ge mina ion [
11
]. The use o elec ical impedance spec oscopy is a echnique ha can p o ide
e y good esul s in he ma u i y s age o ui and ege ables. In his pape , we a e going o ocus on a
Sys em on Chip (SoC) capable o a complex impedance measu emen : he SoC AD5933 [12].
Impedance is a pa ame e o g ea impo ance o he cha ac e iza ion o ci cui s and elec onic
componen s [
13
], as well as he ma e ials used in hei p oduc ion. Impedance (Z) is gene ally de ined
as he o al opposi ion a de ice o ci cui o e s o he low o an al e na ing cu en (AC) o a speci ic
equency, and i is ep esen ed as a complex numbe wi h a g aphic ep esen a ion on a complex
plane. An impedance ec o consis s o he eal pa ( esis ance, R) and he imagina y pa ( eac ance,
X). Impedance can be exp essed by using he ec angula coo dina es in he o m o R +j
·
X, o in he
pola o m as a magni ude and phase angle: |Z|∠Ø [14].
The ins umen s mos commonly used o measu e impedance a e: he LCR me e o LCR b idge
and he impedance analyze . The i s p o ides a simple and exac impedance measu emen o
a speci ic equency alue. Howe e , o componen s o he han pu e induc o s (L), capaci o s
©
,
o esis o s (R), i is inadequa e o de e mine alue. In hese cases, an impedance analyze is used
o measu e and g aphically ep esen he complex impedance o he de ice being es ed o e a
ange o equencies [
15
]. As hey a e high cos de ices [
16
,
17
], he eason why designs using LCR
me e s (which a e cheape ) exis , is o ob ain a sys em impedance analyze combining i wi h i ual
ins umen a ion [12,18].
The e a e a ious con igu a ions o he design o impedance measu ing b idges such as
Sche ing [
19
] and he Maxwell b idge [
20
]. The di icul y wi h hese is ha hey need o ha e
he balance condi ion. Mo eo e , hey a e gene ally used o pu e induc i e o capaci i e impedance
Senso s 2020,20, 5932 3 o 20
measu emen s. In o de o ob ain he complex impedance, elec onic me hods a e used, such as he
ec o al me hod and he me hod using wo quad a u e sinusoidal wa es [
21
,
22
].Ano he way o
measu e he complex impedance is he h ee- ol age me hod [
23
]; howe e , his equi es ol ages o
be aised o he squa e, which makes he measu emen e o s g ea e , in addi ion o he ac ha i
equi es e y p ecise ins umen s o un he measu emen s.
An Impedance/Gain-Phase analyze [
24
] is a measu ing ins umen o g ea alue o he s udy
and design o elec onic ci cui s. This powe ul de ice is capable o ob aining diag ams sepa a ely,
bo h in magni ude and in phase o any ne wo k o elec onic ci cui which has an inpu and an ou pu .
Wi h his in o ma ion, i is possible, o example, o ob ain he ans e unc ion o a speci ic ci cui ,
al hough i s implemen a ion is no known.
An Impedance/Gain-Phase analyze should be capable o ob aining a eliable ampli ude and
phase diag ams co esponding o a speci ic ci cui . In bo h cases, hese a iables will be ep esen ed
acco ding o equency. These ypes o analyze s mus be capable o gene a ing a sinusoidal signal and
di ec ly applying i o he inpu o he ne wo k o be measu ed. Thus, a equency sweep is done on
he ne wo k wi h a speci ic c i e ion ega ding he ini ial, in e media e, inal equency alues, numbe
o poin s, linea o loga i hmic sweep, e c., which is no mally selec ed by he use . To gene a e he
magni ude diag am, i is necessa y o ind he quo ien be ween he ampli udes o he ne wo k ou pu
and inpu o each o he alues o be measu ed in he equency sweep. Fu he mo e, in o de o do
he phase diag am, i is necessa y o ob ain he phase di e ence be ween he ne wo k ou pu and
inpu signals again o each o he equency alues. The e o e, i is ob ious ha in o de o build an
impedance/gain-phase analyze , a sine wa e gene a o is necessa y, a he e y leas , o gene a e a
ci cui equency sweep capable o measu ing ampli ude and o ano he ci cui capable o measu ing
he phase di e ence be ween wo signals.
1.3. P e ious Examples o he Use o Elec ical Impedance in Oli e P oduc ion and O he F ui s
Elec ic conduc i i y has been used (only i s magni ude) o cha ac e ize di e en oli e a ie ies
(Olea eu opa L.) [
25
], speci ically, ou di e en cul i a s: “Picual”, “Manzanilla de Se illa”, “Hojiblanca”
and “Go dal Se illana” wi h he objec i e o es ablishing a ui ma u i y index and, hus o de e mining
he op imal ime o ha es ing based on pa ame e s such as oil yield and quali y, demons a ing ha he
conduc i i y inc eased wi h ui ma u i y and ha each a ie y had an a e age cha ac e is ic elec ic
conduc i i y alue in he las s ages o ma u a ion. P e ious s udies ha e ocused in pa icula on
de e mining ma u i y indexes and quali y pa ame e s [
7
,
26
,
27
], o on ways o slowing he ma u a ion
pe iod, abo e all in climac e ic ui s, wi h he aim o leng hening he pe iod be ween ha es ing and
comme cial consump ion [28].
1.4. Neu al Ne wo ks (NN) o Adjus men and So ing
A i icial neu al ne wo ks a e compu a ional models inspi ed by he beha io obse ed in hei
biological coun e pa s [
29
]. Thei use is widesp ead in an abundance o ields. Focusing on he able
oli e, we can see hei use in [30] o in [31].
In his s udy, we a e going o use wo ypes o neu al ne wo k. On he one hand, a neu al ne wo k
o adjus men [
32
] o e alua e he e ec i eness o his echnique in gene a ing a alid impedance
beha io mode o oli e pulp and, on he o he hand, a neu al ne wo k o so ing [
33
] o dis inguish
be ween oli e a ie ies a di e en empe a u es.
1.5. The In e ne o Things (IoT)
The use o he IoT is widely ex ended nowadays and he e a e nume ous cases ( o example [
34
–
38
])
in p ecision ag icul u e, i iga ion, empe a u e con ol, moni o ing o he ag icul u al p oduc ion
p ocess, in au oma ed oli e chain p ocesses, o in he ope a ion o he pi ing, slicing, and s u ing
machines hemsel es (DRR) [
30
,
31
]. This pape shows he de elopmen o equipmen based on he
Senso s 2020,20, 5932 4 o 20
SoC AD5933 [
12
] which, oge he wi h a neu al ne wo k and an IoT sys em, allows o he analysis o
he s a e o he oli es on he a m o in he ac o y be o e pi ing.
The gene al objec i e se ou by his pape is o de elop an elec ical impedance measu emen
sys em adap ed o able oli es, making use o he SoC AD5933. In o de o do his, wo asks a e going
o be done:
(1)
Impedance modeling h ough neu al ne wo ks o wo a ie ies o oli es (“Go dal Se illana”
and “Hojiblanca”), cu ed in caus ic soda and e men ed in b ine (an indus ial p ocess known as
“Es ilo Se illano”).
(2)
Classi ica ion ia neu al ne wo ks o each oli e a ie y a h ee empe a u es (25
◦
C, 7
◦
C, and
0◦C).
To his end, hese sys ems will be de eloped:
•
A speci ic de ice wi h he SoC AD5933 [
12
], ha includes an I
2
C communica ion in e ace [
39
],
an ex e nal DDS gene a o based on a FPGA XC3S250E-4VQG100C [
40
] o conduc a comple e
sweep om 1 Hz o 100 kHz and wo ADG706 analog mul iplexe s [
41
] o se he impedance
ange o be measu ed. This de ice is con olled by a 32-bi ARM CORTEX M3 AT91SAM 3
×
8 E
mic ocon olle wo king a 84 MHz [42].
•The sys em con ol so wa e using Ma lab p og aming language [43].
•IoT communica ion is based on [44] o gene a e a da abase wi h he ial esul s.
2. Ma e ials and Me hods
2.1. Oli e Va ie ies and Indus ial P ocess Used
The oli e ui (Olea eu opaea L.) [
25
] is an o oid d upe whose size oscilla es om 0.6 o 2 cm
in diame e and om 1 o 4 cm in leng h. This size depends on he a ie y (see Figu e 1 in [
25
]),
he ege a i e
s a e o he ee, he en i onmen al condi ions, and he cul i a ion echniques [
45
].
We used
samples o 100 un ipe oli es om oli e o cha ds (200 ees ha
−1
, Se ille, Spain), unde
i iga ion and non-limi ing nu ien condi ions wi h mechanical ha es ing, and samples o 100 oli es
in b ine om a ac o y in Se ille. In his wo k we used wo a ie ies: “Hojiblanca” and “Go dal
Se illana” eshly picked in class 0, 1, and 2 [
46
] and p ocessed in b ine he “Es ilo Se illano” way.
This ype o oli e, seasoned his way, is p ocessed in ou s ages [47–49]:
•Lye ea men in NaOH 2–4% (p/ ) o 6–12 h
•Rinsed in wa e (12–15 h)
•Fe men ed in b ine (10–12% (p/ ) o 60–300 days)
•Pi ed and s u ed o sliced.
2.2. The SoC AD5933 o Measu e Impedance
Acco ding o he SoC AD5933 da ashee [
12
], “ he AD5933 is a high p ecision impedance con e e
combining an in eg a ed equency gene a o wi h a 12-bi and 1 MSPS analogue- o-digi al con e e
(ADC)”. The impedance o he de ice unde es (DUT) is sampled by he in e nal ADC and is p ocessed
wi h a disc e e Fou ie ans o m (DFT)” [
50
]. The ou pu exci a ion ol age and he measu emen
equency a e o ally p og ammable. Communica ion is done ia an I2C in e ace.
Re iewing he a ailable bibliog aphy con i ms ha he SoC AD5933 has signi ican biological
applica ions, such ha i has been used o moni o he g ow h o cell cul u es [
51
,
52
] in measu emen s
in isola ed cells [
53
], de ec ion o blood clo ing [
54
], biosenso applica ions [
55
], and bio-impedance
measu emen s [
56
–
60
]. Likewise, i is used in he moni o ing o “ echnical objec s”, o example,
o co osion
analysis in s eel s uc u es [
61
,
62
]. In o de o ob ain comp ehensi e in o ma ion abou
he elec ical p ope ies o a measu ed objec and o use a sui able impedance spec um analysis me hod
(equi alen ci cui modelling), impedance mus be measu ed a a wide ange o equencies [63].
Senso s 2020,20, 5932 5 o 20
In Table 1, he echnical da a o a ious impedance me e s based on he SoC AD5933 a e shown.
Only h ee o he de ices desc ibed allow impedance we e o be measu ed in mo e han h ee o de s o
magni ude o equency. The impedance ange measu ed is ypically om 10
Ω
o mo e han
10 MΩ
.
Howe e , in many cases, i does no gi e he exac ange. The majo i y o he impedance me e s
men ioned equi e addi ional analog on -ends o p o ide an adequa e in e ace be ween he SoC
AD5933 and he de ice unde es (DUT) [64].
Table 1. Lis o elec ical impedance me e s based on he SoC AD5933 ( aken om [64]).
Au ho Pu pose F equency Range Impedance Range Maximum E o
C. J. Chen e al. [
51
]
Moni o ing Cell
Cul u es Se o 10 Hz No speci ied No speci ied
T. Schwa zenbe ge
e al. [52]
Moni o ing Cell
Cul u es 100 Hz–100 kHz No speci ied 2%–magni ude,
2%–a gumen
M. H. Wang e al.
[53] (uses an
AD5934)
Measu ing Isola ed
Cells 0.1 Hz–100 kHz 100 Ω–10 MΩA ound 10% o
cell measu emen
J. B oede s e al.
[55]
Biosenso
Applica ion 10 Hz–100 kHz 10 Ω–5 MΩNo speci ied
P. Bogónez-F anco
e al. [57]
Bioimpedance
Moni o 100 Hz–200 kHz 10 Ω–1 kΩ2.5%–magni ude,
4.5%–a gumen
J. Fe ei a e al. [
58
]
Bioimpedance
Elec odes In
Clo hing
5 kHz–450 kHz No speci ied 0.7%– esis ance,
17%– eac ance
C. Ma go e al. [59]
“Embedded”
applica ions o
bioimpedance
1 kHz–100 kHz No speci ied. No
da a
2.5%–magni ude,
1.3%–a gumen
A. Melwin y K.
Rajaseka an [60]
Body composi ion
measu emen s Se o 50 kHz No speci ied 2% (no speci ied)
J. Hoja y G. Len ka
[61,62]
Objec moni o ing
echnique 0.01 Hz–100 kHz 10 Ω–10 GΩ1.6%–magni ude,
0.6%–a gumen
O he au ho s [
65
–
67
] p oposed modi ica ions in he o iginal opology p o ided by he
manu ac u e wi h he use o a mul iplex sys em o adjus he ange o he impedance measu emen ,
al hough his does no include changes in he sou ce clock inpu in o he SoC AD5933. In [
68
] he
ope a ion o he SoC AD5933, he ha dwa e and so wa e de eloped, and he IoT sys em a e desc ibed.
2.3. Neu al Ne wo ks o Modeling and So ing
Two ypes o neu al ne wo ks we e used om he Ma lab lib a ies:
•
A neu al ne wo k o adjus men , “ i ne ” [
32
], allows a desc ip ion o he e olu ion o he complex
impedance in he pulp o 2 a ie ies o oli es o be ob ained. I is a conside able imp o emen
o e he Hayden model [69].
•
A so ing ne wo k, “pa e nne ” [
33
], o dis inguish be ween 6 cases (2 a ie ies and 3 empe a u es)
in un ipe and ano he 6 cases (2 a ie ies and 3 empe a u es) in oli es p ocessed he “Es ilo
Se illano” way.
3. Resul s
Th ee e i ica ion es s o he de eloped ha dwa e ha e been ca ied ou (Sec ions 3.1–3.3) as well
as a s udy on he e ec o a ie y on elec ical impedance in un ipe oli es (Sec ion 3.4) and on oli es in
b ine (Sec ion 3.5). A model wi h neu al ne wo ks on he e olu ion o impedance in un ipe and b ined
oli es o he wo a ie ies s udied in Sec ion 3.6. and a classi ie based on neu al ne wo ks capable o
dis inguishing be ween 6 di e en cases in un ipe oli es was ained (Sec ion 3.7.1), in b ined oli es
(Sec ion 3.7.2), and inally (Sec ion 3.8) he IoT sys em used is shown.

Senso s 2020,20, 5932 6 o 20
3.1. Impedance Me e Ve i ica ion Tes ing: DUT Made Up o a Pu e Resis ance o 10 kΩ
A es has been done using a pu e esis ance o 10 K
Ω
, he esul s a e in Figu e 1. The objec o he
es is o make su e ha he equipmen is wo king co ec ly. As can be seen, he answe is he same in
bo h he magni udes as in he phase h oughou he sweep om 1 Hz o 100 kHz.
Figu e 1.
Pola diag am: Comple e sweep om 1 Hz o 100 kHz wi h ZIN =10 K
Ω
(Magni ude 10 k
Ω
,
Phase 0◦).
3.2. Impedance Me e Ve i ica ion Tes ing: DUT Comp ised o a SERIAL RLC Ci cui
We conduc ed a es on he SERIAL RLC ci cui wi h an induc ance o L =56 mH, C =1500 pF
and R =5.1 k
Ω
, wi h Zcal =10 k, ZBF =10 k, Range 1: 2 Vpp, PGA =
×
1, Mul iplie =
×
1 om 1 Hz o
100 kHz (see Tables 1 and 2 in [68]).
Fo he es , h ee elemen s we e connec ed in se ies o build a ypical RLC ci cui . The heo e ical
esonance equency is:
o=
1
2·π·√L·C
=
1
2·π·p56 ×10−3×1500 ×10−12
=17365.22 Hz (1)
A low equency p edomina es he capaci i e pa wi h nega i e phases ha end o
−
90
◦
. In he
p oximi y o he esonance zone, he phase ended o ze o and om ha momen he induc i e pa
began o p edomina e, he phase in ha case posi i e ends o 90
◦
. The heo e ical and expe imen al
esul s a e shown in Figu e 2. The small disc epancies be ween heo e ical and expe imen al da a a e
due o he ole ance o he componen s used in he eal es .
Senso s 2020,20, 5932 7 o 20
Figu e 2.
Pola diag am o he es wi h SERIAL RLC ci cui be ween 1 Hz and 100 KHz. The blue
alues a e measu ed and he ed ones a e heo e ical.
3.3. Impedance Me e Ve i ica ion Tes ing: DUT Comp ised o a PARALLEL RLC Ci cui
The es on he PARALLEL RLC ci cui wi h an induc ance o L =56 mH, C =1500 pF and
R=5.1 kΩ
, wi h Zcal =10 k, ZBF =10 k, Range 1: 2 Vpp, PGA =
×
1, Mul iplie =
×
1 om 1 Hz o
100 kHz (see Tables 1 and 2 in [68]).
Fo his es , h ee elemen s ha e been connec ed in pa allel o build a ypical RLC ci cui in
pa allel. The heo e ical equency will be he same as in he p e ious es .
The heo e ical and expe imen al esul s a e shown in Figu e 3. Once again, he di e ences a e
due o he ole ance o he componen s used.
Figu e 3.
Pola diag am o he es wi h he PARALLEL RLC ci cui be ween 1 Hz and 100 kHz. The
blue alues a e measu ed and he ed ones a e heo e ical.
Senso s 2020,20, 5932 8 o 20
3.4. Tes on Un ipe Oli es: The E ec o Oli e Va ie y on Elec ic Impedance
This s udy has deal wi h oli e samples om he “Go dal Se illana” and “Hojiblanca” a ie ies,
shown in Figu e 4, om wo oli e ees si ua ed side by side and he e o e subjec o he same
en i onmen al and wa e ing condi ions. These samples we e ha es ed on he same day a he same
ime (16/06/2019).
Figu e 4.
(
a
) “Go dal Se illana” and (
b
) “Hojiblanca” oli e a ie ies du ing he elec ical
impedance measu emen .
In Figu e 5, he e olu ion o he impedance p o ile ob ained (an a e age o 100 es s) appea s
p esen ed as i s componen s X-R o un ipe oli es o bo h a ie ies a h ee empe a u es: 0
◦
C (blue),
7◦C (yellow), and 25 ◦C ( ed).
As can be seen, hey p esen a cha ac e is ic p o ile di e en ia ed bo h by empe a u e and
maximum alues, he “Hojiblanca” being he one wi h highe alues in bo h componen s X, R, and
he eby he module Z, bo h a 0
◦
C and 7
◦
C, while a 25
◦
C i s p o ile is simila o he “Go dal
Se illana”.
P e ious es s ha e demons a ed ha hese impedance p o iles do no adjus well o models o
he ype desc ibed [
70
] (see Figu e 3b o said ci a ion) wi h minimum a X close o ze o. Con e sely,
in un ipe oli es a a low equency, he e a e high alues in bo h R and X ( ed ci cles on he g aphs).
Likewise, wo ela i e minimums can be obse ed in he eac ance X alue (g een diamonds) a 7
◦
C
and 25
◦
C. The end on he g aph o 0
◦
C sugges s ha a equencies o e 100 kHz i would also exis
in his case.
Senso s 2020,20, 5932 9 o 20
Figu e 5.
E olu ion o he impedance in (
a
) un ipe “Go dal Se illana” and (
b
) “Hojiblanca” a ie ies a
3 empe a u es: 0 ◦C, 7 ◦C, and 25 ◦C (a e age o 100 es s). The ed ci cles co esponds o =1 Hz.
One o he p oblems ha some imes appea s is dis inguishing be ween he un ipe a ie ies,
due o
he ac ha hei ou wa d appea ance and size cause doub . This es demons a ed how hese a ie ies
(un ipe) a ec he elec ical impedance he same as he es o he pa ame e s (especially empe a u e).
This sys em would allow he sample a ie y o oli e o be iden i ied om he elec ical impedance
wi hou using o he cha ac e ized pa ame e s.
In Figu e 6, he impedance spec um o bo h a ie ies is shown oge he (in pola diag am).
Each one
has a cha ac e is ic p o ile a each empe a u e and he maximum di e ence is ound a low
equencies, which could se e o dis inguish be ween un ipe oli e a ie ies as is also indica ed in [
25
].
Figu e 6.
F equency sweep o measu e he elec ical impedance o he “Go dal Se illana” and
“Hojiblanca” a ie ies when un ipe (a e age alues om 100 es s).
3.5. Tes on P ocessed Oli es: The e ec he Oli e Va ie y Has on Elec ical Impedance in Oli es P ocessed he
“Es ilo Se illano” Way
Jus as wi h un ipe oli es, i is some imes di icul o dis inguish be ween p ocessed a ie ies
because o hei shape, size, and special colo (due o he chemical p ocesses hey unde go) and hey
Senso s 2020,20, 5932 16 o 20
On he o he hand, o each hese esul s, he design o a ha dwa e has been chosen ha has
allowed us o ob ain he maximum bene i s o he SoC AD5933:
•
A ci cui implemen ing an SoC AD5933 has been de eloped wi h all he pe iphe al elemen s
necessa y o i o un. This p o o ype includes a pai o ADG706 analog mul iplexe s in o de o
con e he ange in he impedance module o be measu ed.
•
In o de o achie e he maximum esolu ion in he DFT, a DDS based on an FPGA has been used
o gene a e a clock signal o be p og ammed a will acco ding o he limi s o he equency sweep
o be ca ied ou du ing he impedance measu emen .
•
P og amming he main applica ion has been done in Ma lab. In o de o con ol all o he elemen s,
an ARM CORTEX M3 (AT91SAM3X8E) mic ocon olle has been used wi h an A duino DUE,
implemen ing all o he i mwa e necessa y o con ol he ha dwa e. Las ly, he Picoblaze ou ine
con ol embedded in he FPGA o he DDS has been implemen ed in ASM.
•
The esis ance es s and he RLC se ies/pa allel ci cui s ha e shown ha he sys em wo ks p ope ly.
•
The e is a unc ional limi a ion o he chip whe e he in e nal DSP speed is p opo ional o he
clock speed applied ex e nally. In hese ci cums ances, o he low equency measu emen ( om
1 Hz o 30 Hz), a 25 kHz clock has been used which, compa ed o he equency used (16 MHz),
makes he measu emen p ocess 640 imes slowe a low equencies.
•
The ci cui buil is expe imen al and, in o de o use i di ec ly on he a ms whe e he c op
is loca ed, a e sion capable o wi hs anding hose wo king condi ions ough o be p oduced.
Likewise, he applica ion should be an app, o example on a cell phone o a able , whe e i could
connec o he compu e ia Blue oo h.
•
One possible op ion is o implemen all he ou ines h ough a mic ocon olle embedded in he
FPGA, using a p og amable mic ocon olle di ec ly in C ( o example, Mic oblaze) in his case.
•Finally, among he u u e a eas o wo k, we a e conside ing:
•
Inc easing he equency ange o 25 MHz (likely on a sys em which allows i o go o e
100 kHz
)
wi h he objec i e o seeing i , a e ha poin , hey a e s anda d applica ion models like in
Hayden’s.
•S udying o he oli e a ie ies o comme cial ele ance like “Manzanilla” o “Cace eña” oli es.
•S udying o he indus ial ea men s like he oxidized black oli e (Cali o nia s yle).
•
Running an analysis which co ela es he b eakage pe cen age in DRR machines di ec ly wi h he
measu ed impedance alue o di e en a ie ies, p ocesses, and empe a u es.
Fu u e s udies will include he applica ion o his me hodology in o he ui s such as oma o
o che y.
Au ho Con ibu ions:
Concep ualiza ion, A.M.L.; Da a cu a ion, J.M.M.L.; In es iga ion, A.M.L. and R.E.H.F.;
Supe ision, J.M.M.L., A.M.L. and R.E.H.F.; Valida ion, J.M.M.L., A.M.L. and R.E.H.F. All au ho s ha e ead and
ag eed o he published e sion o he manusc ip .
Funding: This esea ch ecei ed no ex e nal unding.
Con lic s o In e es : The au ho s decla e no con lic o in e es .
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