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Electronic pH MetersH ms mloyg glss lod usul o s H msum
bu qu qu lbo, o sog d hdlg o su uy
d lbly. Th l o whh suh ms o s bsd o h
h wh glss o omoso ss wo quous soluos hvg
d hydog o oos, volg s dvlod bw h wo
s o h glss. Th lo m sl s smly vy ssv volm,
whh msus h volg bu s lbd ms o H us sd o vols.
Maintenance
by Bob Taylor - Chemist or Flairorm Australia
Figure 1: Popular styles o pH meters: availability
ranges rom the more expensive laboratory
grade (let), to the cheaper pocket sized (right).
C o p y r i g h t © 2 0 0 8 w w w . f a i r o
r m . c o m
pH Meter
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Accuracy problems with pH Meters
No h ds bg oly lbd hs b my
qu x h d H ms wll odu
sgly d H dgs o h sm soluos. Ths
s slly u o low quly lods bus hy
sod o oh ss h lohmlly sml o
hydog os, suh s sodum. Fo hs so gow g
H dgs dg by mo h 0.5 us wh sg
u sml wh wo d H ms h hv b
oly lbd. No h H dos o gv ls
dgs wh ololss smls bus hy wll oly sod
o hydog os.
Storage of pH Electrodes
Fo H m wh sgl ombo lod o wok
oly h mus b ll oo bw h
lod llg soluo (usully ossum hlod – whh s
llly oduv) d h sml soluo. Ths s hvd
Calibration of pH Meters
To su h uy, H ms mus b gully lbd
o uy usg sdd H bu soluos h md o
olly gd . Ths sbl soluos h
ossss s H vlu. I s ssl o lb usg
ls wo H bus h d H by ls h H us
ov h g bg usd. Fo hydoos H bu 4.0 dH bu 7.0 h dl lbo sdds o us.
Som muus lm h H ms qu oly
sgl o lbo. Howv, h lm s smly o
jusbl uy s ds. Th us o wo H bu
sdds sus h h lbo slo s obd. I hs
uo s o k wh h lod s l ld
H bu 4.0 soluo, h m wll ylly d, o xml,
4.4, sd o 4.0. Ths ol oblm b vodd by
usg boh h H 7.0 d 4.0 bus.
How to Calibrate
Follow you H m muu’s suos.
Alvly, su o lb s wh H bu 7.0
ollowd by H bu 4.0. To do hs, s h lod
dslld w d gly shk o h xss w. Th,
mms h lod H bu 7.0 soluo o ls wo
mus bo djusg so h ds 7.0. Flly h
odu wh H bu 4.0 djusg so h ds 4.0. To
v omo o h H bus, d oo o
smll o o om h bov lbo, d dsd
o usd.
Common Mistakes Made WhenUsing Electronic pH Meters
1. Bo msug h H, su h h u s wll
sd, slly H u d dow usd. Ths s o
o h mos ommo msks md wh sg H o
oduvy. Also, su h smlg o s l.
2. See Figure 2 - Wh h H lod s ld sml,
you my o h h dg vs o som m (myb
svl mus) bo sg o l vlu. Th my b
d xss o 1.0 H u bw h l d
l H vlu. S h l vlu wll b h mos u,
mk su you w log ough o h dg o sblz.
Howv, o h so o lg.
Figure 3:
Do not immerse the electrode deeper than 20mm.
Figure 4:
Always clean the electrode
with distilled water ater use
- No. 1 maintenance tip or
prolonged electrode lie!
Figure 5:
Always keep pH electrodes
immersed in a “ storage”
solution when not in use.
Figure 2:
Stir nutrient tank well beore sampling.
Then leave the electrode in the sample
or a ew minutes beore switching the
meter on and taking the measurement.
Copyright ©2008 www.fairorm.com
Copyright ©2008 www.fairorm.com
Copyright ©2008 www.fairorm.com
3. Do o mms h lod h sml o dh h
xds h lvl o h llg soluo sd h lod
(Figure 3). S s o ossbl o vw h dh o
h llg soluo my ok szd ms, mms
h lod o dh o o mo h 20 mllms.
Exdg hs dh m h sml soluo o w
bk o h lod sl sulg u dgs.
4. O h dg hs b k, mmdly mov h
lod om h sml d s wh dslld w
(Figure 4). Flu o do so wll us d doo
o h lod d s h d d quy o
ou m – s so o lg. Whls o
us, su o so h lod (Figure 5) oly
omuld sog soluo – s so o sog.
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v h us o oous o wk (Figure 6) h glss wll
sg h llg soluo hmb om h sml.
Boh hs dvs llow h (vy slow) fow o h llg
soluo o h sml soluo.
Th mos ommo us o H m lu s du o
blokg o hs oous o wk. Ths s usully usd by
dy sog o h lod o lvg h lod mmsd
o oo log od soluos. Dy sog uss
dhydo o boh h glss lod d o
o sls wh h ss o h sl (Figure 7). Th
osqus dg d, slow sos ms d
dsd ssvy sulg (loss o uy d so).
To vod hs oblms h lod mus b mly
sod (Figure 5) slly omuld sog soluo.
No h w o H bus o subl o sog o
H lods.
Rgul lg wll mxmz lod om d
su log wokg l. Som subl ls :
• Og omo - us mld lqud dg,
o*, mhyld s o oluol*. I oluol s ssy,
s subsquly wh o o mhyld ss d
lly w. • Iog omo – us dlu o
hydohlo d.
I hydoos, bus boh og d og
omos d o o-ou, s bs o us ll-
uos l.
* No h som ls my k lod hdw
- ully ls. Tho, su o hk wh h
lod’s muu bo odg.
pH Indicators
Alhough H dos my o lwys dsgush
bw H o, sy, 5.2 d 5.3, wd g olo
H dos hvg good olo soluo b:
• Fs
• Exmly u
• Sml
• Rlbl
• Us dly
• Eooml
As od, H ms qu os
u-k. Clg, lbg d o
sog mus b do o gul bss,bu v h my o gv lbl
dgs.
pH Meter Maintenance
Figure 6:
Schematic layout o glass pH
electrode. Loss o accuracy is
invariably explained by dierent
degress o blockage o the ‘rit’ or
‘wick’ - oten caused by dry storage.
Testing o oily or harsh chemicals
(eg. pH Up or concentrated
nutrient), or ailure to rinse the
electrode properly ater use.
Figure 7:
Arrow highlights contamination on
this ‘rit’ (or wick). The hydrogen
ion sensitive glass ‘bulb’ containing
the measuring cell electrode can be
seen to the right o the arrow.
Copyright ©2008 www.fairorm.com
Copyright ©2008 www.fairorm.com
Cleaning pH Electrodes
Th d glss o H m lods vbly bom
omd wh mus (Fg 1.8b) usg symoms suh
s dg d, slow sos ms d dsd ssvy
(loss o uy d so). Como my b so
sv h -lbo s o ossbl whou o lg.
Mmz hs oblm by lg olly oblm
w smls (.. gsy o hghly ubd) o o omg
H msum. Avod lg lods oly soluos
s hy o h lod. Fuhmo, vod msug
(o lvg lods o oo log) hsh hmls h
hghly us (H U, sl ddvs) o od soluos
lk w us. Ths dmg lods d/o s
h d o lod m.
MY