Apera Instruments SX721 User manual

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SX721 Portable pH/ORP Meter
User Manual
APERA Instruments (Europe) GmbH
aperainst.de

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Table of Contents
1Brief Instruction...............................................................................................................- 3 -
2Technical Specifications....................................................................................................- 3 -
3About the Meter.............................................................................................................. - 4 -
4What’s in the kit ..............................................................................................................- 6 -
5Preparation .....................................................................................................................- 6 -
6pH Measurement.............................................................................................................- 7 -
6.1 pH Electrode .............................................................................................................- 7 -
6.2 pH Calibration ...........................................................................................................- 8 -
6.3 Notes about pH Calibration .......................................................................................- 9 -
6.4 Sample Test...............................................................................................................- 9 -
6.5 Recommended pH Electrodes for Different Applications .......................................... - 10 -
6.6 Parameter Setting ................................................................................................... - 11 -
6.7 Cleaning pH Electrode ............................................................................................. - 13 -
6.8 The Self-diagnose Information................................................................................. - 13 -
6.9 Notes about pH ....................................................................................................... - 14 -
7ORP Measurement: ....................................................................................................... - 14 -
8Limited Warranty........................................................................................................... - 16 -
Scan the QR code below to watch the tutorial video on Youtube.

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1 Brief Instruction
Thank you for choosing Apera Instruments SX721 Portable pH/ORP Meter (will be called “the meter” in
short in the following content). Before using the meter, please read this instruction manual carefully in
order to help you properly use and maintain it.
The meter can measure the parameters of pH, ORP, and temperature of water solutions with high
accuracy. It is suitable for various applications in different industries e.g., water treatment, aquaculture,
horticulture, pools and spas, beverage making, mining, power plants, environmental monitoring, etc.,
especially ideal for in-field use.
The meter has the following features:
1.1. Built-in microprocessor chip with the intelligent functions of auto. calibration, auto. temperature
compensation, auto. salinity compensation, manual baromatric pressure compensation, data storage,
function settings, auto. power off, and low voltage display etc.
1.2. Adopts digital filter technology to intelligently improve meter’s response speed and accuracy. The
smiley face icon will appear when the reading is stable.
1.3. Pure water modes available for pH, significantly increasing the accuracy in pure water measurement.
1.4. Meter’s LCD screen has clear and bright backlit display.
1.5. Built-tough. IP57 waterproof and dust-proof.
2 Technical Specifications
2.1 pH
Measurement range
(-2.00 to 19.99) pH
Resolution
0.1/0.01 pH
Accuracy
Meter: ±0.01pH; Overall: ±0.02pH
Input current
≤2×10-12 A
Input impendance
≥1×1012 Ω
Stability
±0.01 pH/3h
Temp. compensation range
(0 to 100) °C (automatic)

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2.2 ORP (mV)
Measurement range (mV/ORP/EH)
-1999mV to 0 to 1999mV
Resolution
1mV
Accuracy
Meter: ±0.1% FS, Overall: ±15mV
2.3 Other Technical Parameters
Data storage
200 sets
Data content
Serial number, measurement value, measurement unit, and
temperature
Power Supply
Two AA alkaline batteries (1.5V x2)
Dimensions and weight
Meter: (65×120×31) mm/180g
Complete Kit: (255 x 210x 50) mm/1380g
Quality and safety certification
CE, ISO 9001:2015
2.4 Working Condition
Working temperature
5 to 35°C
Working humidity
≤85%
IP rating
IP57 water-resistant
3 About the Meter
3.1 Screen Display
① —— Parameter icon ② —— Measurement value
③ —— Serial number and icon as measurement to be saved and recalled and indication icon for
special states.

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M+ — measurement value to be saved; RM — Saved data to be recalled;
④ —— Measurement unit ⑤ —— Temperature measurement value and unit
⑥ —— Measurement stabilization icon ⑦ —— Electrode calibration indication icon
⑧ —— Indication icon of low battery power; appears when the voltage is less than 2.6V, calling
attention to replace the batteries.
3.2 Keypad
The meter has 5 operation keys in total.
Short press: press time <1 seconds; Long press: press time >2 seconds
3.2.1. — Short press to power on or off.
3.2.2. — Calibration key
(a) When in measurement mode, short press to enter calibration mode.
(b) When in parameter setting mode, short press to make changes.
3.2.3. — Function key
(a) In measurement mode, short press (<1.5s) to switch between and . Long press
to enter parameter setting (P1, P2, P3…)
(b) In other measurement mode, short press this key to enter the parameter setting mode (P1, P2, P3…)
3.2.4. — Back light and confirmation key
(a) In measurement mode, short press to turn on or ff the back light.
(b) In calibration mode or the parameter setting, press this key to make confirmation, and return to
measurement mode.
(c) When in mode, hold this key to change pH resolution: 0.01 → 0.1 pH in turn. Release key when
you confirm the selection.
3.2.5. — The key for data saving and recalliing
(a) When in measurement mode, short press to save the measurement data; Long press to recall the
saved data.
(b) When in parameter setting mode, press the key to make changes.

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3.3 Data Log, Recall and Delete
3.3.1. Save the measurement:
In measurement mode, when the reading is stable and stays on screen, short press to save
the measurement data. M+ icon and the data serial number will show up on the upper right corner. The
meter can store up to 200 sets of data.
3.3.2. Recall saved data:
(a) In measurement mode, long press , the meter will recall the last saved data and the serial
number. RM icon will appear in the upper right corner of the screen.
Short press or again, the meter will recall all the data in turn, hold or
to quickly review the data.
(b) In data recalling mode (RM and serial number in the lower right corner), short press to return
to measurement mode.
3.3.3. Delete data:
In data recalling mode, hold for 5 seconds, CLr will show up for 2 seconds, meaning that all the
saved data have been eliminated. Then the meter will return to measurement mode.
4 What’s in the kit
SX721 pH/ORP meter *1
201T-S plastic pH/ATC three-in-
one combination electrode *1
301Pt-S plastic ORP
combination electrode *1
Carrying case *1
Screw driver *1
Spare AA batteries *2
User manual *1
pH standard buffer solution (pH 4.00, pH 7.00, pH 10.01) *1
50ml bottle/each
5 Preparation
What you need in addition to what’s in the kit:
Pure water (RO, distilled or deionized water) for rinsing off the electrode.

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6 pH Measurement
Short press to turn on the meter. Connect 201T-S pH electrode to the meter (See Section 5 for
connection tutorial). The meter will automatically enter pH measurement mode.
6.1 pH Electrode
The meter comes with the 201T-S 3-in-1 combination electrode with a built-in temperature sensor, which
enables automatic temperature compensation. This electrode is only suitable for general water
solutions’ pH testing. Please refer to Section 6.5 for ideal pH electrodes to use for other applications. A
3M KCL storage bottle comes with the electrode, which is for storing the electrode when not in use to
keep the sensitivity of the probe.
6.1.1 Technical Specifications of the 201T-F pH Electrode
Measurement Range: 0 - 14 pH, 0 – 80°C (32 – 176˚F); Junction: Single Ceramic
Reference Electrode: Ag/AgCl Connector: 8-pin; Temperature unit: 30K Thermistor
Size: ø12*160 mm; Cable length: 1 meter

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6.1.2 Use the Electrode
Screw off the KCL storage bottle, and put it aside (do not dump or spill the KCL solution). Rinse the
electrode with distilled or deionized water. Shake off excess water or blot-dry with clean tissue or kimwipe.
Stir the electrode for a few seconds after it’s dipped into the test solution and then hold it still. Wait for the
reading to get fully stabilized ( appears and stays) and then take the measurement. When the test
is finished, place the electrode in the storage bottle and tighten the cap to keep the sensitivity of the pH
sensor.
6.2 pH Calibration
6.2.1 After powering on the meter, short press to enter calibration mode, c1 flickers on LCD,
indicating the meter enters the first point calibration.
6.2.2 Rinse off the pH electrode in pure water and remove excess water, then insert it into the pH7.00
buffer solution, make a quick stir and then hold it still. When the reading is stabilized and stays on
screen, short press again to finish the 1st point calibration. “7.00 pH” will start flickering and a
flickering c2 will show up, indicating the 1st point calibration has been finished and the meter is entering
the 2nd point calibration.
6.2.3. Rinse off the pH electrode in pure water and remove excess water, then insert it into the pH 4.00
buffer solution, make a quick stir and then hold it still. When the reading is stabilized and stays on
screen, short press again to finish the 2nd point calibration. “4.00 pH” will start flickering and a
flickering c3 will show up, indicating the 2nd point calibration has been finished and the meter is entering
the 3rd point calibration.
6.2.4. Rinse off the pH electrode in pure water and remove excess water,
then insert it into the pH 10.01 buffer solution, make a quick stir and then
hold it still. When the reading is stabilized and stays on screen, short
press again to finish the 3rd point calibration. “10.01 pH” will start
flickering and then the meter will return to measurement mode.
will show up at the bottom left (see picture 4-1), indicating all 3 calibrations are finished.

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6.3 Notes about pH Calibration
a) Keeping the freshness and cleanliness of calibration buffers is essential for accurate pH
measurement. The small bottles of pH buffers come with the meter should be replaced within 3
months after opening. The new buffer solutions should be made by a legitimate lab supply
manufacturer. Avoid sunlight and air contact when the buffers are not being used, and store at
room temperature.
1) This meter can adopt random 1-point, 2-point or 3-point automatic calibration. During calibration,
short press to return to measurement mode. When the measurement accuracy is ≤ ±0.1pH,
choose a buffer that’s close to the estimated measurement range and perform 1-point calibration
would be good. Choose pH 4.00 and pH 7.00 to calibrate if the measurement range is within the
acidity range (<pH 7) and choose pH 7.00 and pH 10.01 to calibrate if just within the alkalinity
range (>pH 7).
2) Choose 3-point calibration to achieve a more accurate measurement if the measurement range
is wide, or if the electrode has not been used for long. When connecting a new pH electrode, it
must be calibrated at 3 points.
3) The frequency that you need to calibrate your meter depends on the tested samples, condition of
electrodes, and the requirement of the accuracy. For high-accuracy measurements (≤ ±0.02pH),
the meter should be calibrated before test every time; For ordinary-accuracy measurements
(≥±0.1pH), once calibrated, the meter can be used for about a week or longer. In the following
cases, the meter must be re-calibrated:
•The electrode hasn’t been used for a long time or a new electrode is connected.
•After measuring strong acid (pH<2) or strong base (pH>12) solutions.
•After measuring fluoride-containing solution and strong organic solution.
•There is a significant temperature difference between the test sample and the buffer solution.
6.4 Sample Test
Power on the meter. Connect the pH electrode and the meter goes to pH measurement mode
automatically. Screw off the KCL storage bottle. Rinse the electrode with pure water. Shake off excess
water or blot-dry with clean tissue or kimwipe. Stir the electrode for a few seconds after it’s dipped into
the sample solution and then hold it still. Wait for the reading to get fully stabilized ( appears and
stays). Then save the measurement by pressing .
According to the pH isothermal measurement principle, the closer the test sample’s temperature is to the

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calibration solution’s, the higher the accuracy of the measurement. This principle is recommended to
follow for the best result. For example: If you have to test at 150°F, we recommend warming up the
calibration solutions to the same temperature before performing calibration in order to get the most
accurate readings.
6.5 Recommended pH Electrodes for Different Applications
Application
Ideal Apera pH Electrodes
General water solutions
201T-S, LabSen 211, LabSen 213
Beverage, beer, wine
LabSen 211, LabSen 213
Low ionic strength solutions (RO water, distilled water,
deionized water…)
LabSen 801, LabSen 803
Liquid food (milk, cream, yogurt, jam, sauce, etc.)
LabSen 821, LabSen 823
High-Temperature solutions
LabSen 841, LabSen 861
Low-temperature liquid
LabSen881
High salinity solutions
LabSen 841
Complex and caustic solutions (e.g. electroplating)
LabSen 861
Raw meat
LabSen 761, LabSen 763
Micro sample testing
LabSen 241-6, LabSen 241-3
Cosmetics, skincare products
LabSen 851-1, LabSen 851-S
Soil
LabSen 551, LabSen 553
Solid or semi-solid samples (cheese, dough, fruits, meat
products, etc.)
LabSen 251, LabSen 751, LabSen
753
Strong acid solutions, HF containing solutions (HF
concentration<1%)
LabSen 831
Strong alkaline solutions
LabSen 841
Surface test (skin, paper, carpet, etc.)
LabSen 371
TRIS buffer solutions
LabSen 213, LabSen 223
Viscous solutions
LabSen851-S, LabSen 851-H
Wastewater or emulsion
LabSen 333

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* An 8-pin to BNC convertor (AI7103) is required to connect LabSen pH electrode to this meter.
* Visit aperainst.de or contact us at [phone] for more details.
6.6 Parameter Setting
Table (4-1)
Prompt Mark
Parameter Setting Items
Code
Parameters
P1
pH buffer solution series selection
USA (U.S.A series)
NIS (NIST series)
CH (China series)
P2
Pure water pH temperature
compensation setting
OFF-On (shut-set)
P3
Ammonia added pure water pH
temperature compensation setting
OFF-On (shut-set)
P4
Temperature unit setting
°C - °F
P5
Back light display time setting
0-1-3-6min
P6
Auto power off setting
0-10-20min
P7
Restore to producer setting
OFF-On
6.6.1 pH buffer solution series selection (P1)
(a) Long press , meter enters P1 mode: see picture (4-2).
(b) Press or to choose buffer solution series:
(U.S.A series) — 1.68, 4.00, 7.00, 10.01and 12.45 pH
(NIST series) — 1.68, 4.01, 6.86, 9.18 and 12.45 pH
(China series) — 1.68, 4.00, 6.86, 9.18 and 12.46 pH
(c) Press to enter next parameter setting or press to confirm and return to measurement
mode.
6.6.2 Pure water pH temperature compensation setting (P2)
(a) Short press in P1, the meter enters mode P2, see picture (4-3).
(b) Press or to choose
(pure water pH temperature compensation setting) or
(c) Press to enter next parameter setting or press to confirm
and return to measurement mode.
(d) The factory default setting is OFF
Note: will appear in the upper right corner of the LCD if pure water temperature compensation

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function is set.
6.6.3 Ammonia added pure water pH temperature compensation
setting (P3)
(a) Short press in mode P2 to enter mode P3, see picture (4-4).
(b) Press or to choose (ammonia added pure water pH
temperature compensation setting) or
(c) Press to enter next parameter setting or press to confirm and return
to measurement mode.
(d) The factory default setting is OFF
Note: If the ammonia pure water pH temperature compensation function is set,
will appear in the right upper corner of the LCD when in measurement mode.
6.6.4 Temperature unit °C/°F setting (P4)
(a) Short press in P3 to enter P4, see picture (4-5).
(b) Press or to choose temperature unit: °C or °F.
(c) Press to enter next parameter setting or press to confirm
and return to measurement mode.
6.6.5 Back light display time setting (P5)
(a) Short press in P4 to enter P5, see picture (4-6).
(b) Press or to choose the time of back light auto off: 0min,
1min, 3min or 6min. The back light will be closed if choosing 0 min.
(c) Press to enter next parameter setting or press to confirm
and return to measurement mode.
(d) The factory default setting for P5 is 1 min.
6.6.6 Auto power off time setting (P6)
(a) Short press in P5 to enter P6, see picture (4-7).
(b) Press or to choose the time: 0min, 10min or 20min. The
auto power off function will be closed if choosing 0 min.
(c) Press to enter next parameter setting or press to confirm
and return to measurement mode.
(d) The factory default setting for P6 is 10 min.

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6.6.7 Restore to factory default setting (P7)
(a) Short press in P6 to enter P7, see picture (4-8).
(b) Press or to choose , meaning that the parameters
have been restored to the producer setting mode, and return to
measurement mode after 2 seconds. Returning to factory default setting
is to restore the meter to theoretical value (zero potential pH is 7.00, slope
is 100%), and set all the parameters to default settings. When the meter’s calibration or measurement is
performing abnormally, users can use this function, and then calibrate and test again. Please note that
this function is irreversible once used.
6.7 Cleaning pH Electrode
1) The measurement is only as accurate as the electrode is clean. Always thoroughly rinse off the
electrode before and after each test with pure water.
2) For tough contaminants, soak the electrode in Apera electrode cleaning solution (AI1166) for at
least minutes. Then use a soft brush to remove the contaminants. Afterwards, soak the electrode
in 3M KCL soaking solution for at least 2 hours. Rinse it off, then re-calibrate the tester before
using again.
3) For other special contaminants, refer to the table below:
Contamination
Cleaning Solution
Inorganic metal oxide
Dilute acid less than 1mol/L
Organic lipid, protein containing samples
Apera cleaning solution (AI1166)
Resin macromolecule
Dilute alcohol, acetone, ether
Paints
Dilute bleacher, peroxide
6.8 The Self-diagnose Information
During usage, the following icons may show up on LCD. This is the meter’s self-diagnose information,
which can help you understand what may go wrong with the meter or electrode.
6.8.1. The stable icon -2.00 pH or 19.99 pH — this icon appears when the pH value exceeds the
measurement range. This icon will also show up when the electrode is not well connected with the meter
or when the electrode is not insertd into solution. This is a normal phenomenon.
6.8.2. — Electrode offset out of range (<-60mV or >60mV)

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6.8.3. — Electrode slope out of range (< 85% or >105%)
When or shows up:
1) Make sure there is no damage on the electrode’s glass bulb (if so, an electrode replacement is
necessary). Check if there is air bubble inside the glass bulb. If so, shake the electrode with force
for several seconds to remove the bubble.
2) Check the quality of buffer solution. Make sure it’s fresh and clean and conforms to the meter’s
buffer series setting.
3) Set the meter to factory default setting mode (refer to section 6.6.7), then recalibrate it.
If the meter is still not working after the above checkings, it’s time to replace a new pH electrode or contact
us at [phone] or [email protected] for help.
6.9 Notes about pH
1) Never store pH electrode in pure water as it will damage the electrode. Always store the electrode
in 3M KCL soaking solution (AI1107).
2) If you find any air bubble in the glass bulb of the pH sensor, simply shake the probe with force for
a few times to remove it. The existence of an air bubble in the glass bulb will significantly decrease
the stableness of measurement.
3) pH electrode is technically a chemical battery. Every pH electrode will eventually die even if you
don’t use it at all. The typical service life of a pH electrode is 1-2 years depending on how you
use and maintain it. We recommend replacing your pH electrode after one year of use to ensure
the best result.
4) Always keep the meter’s connector clean and dry, otherwise it may lead to an inaccurate
measurement. If contaminated, clean the connector with alcohol prep pads and blow-dry.
7 ORP Measurement:
7.1 Sample Test:
5.1.1. Press to power on, connect the ORP combination 301 Pt-S electrode (See Section 5 for
connection tutorial), the meter will enter ORP measurement mode automatically.
5.1.2. Screw off the storage bottle. Rinse the electrode with pure water. Shake off excess water or blot-
dry with clean tissue or kimwipe. Stir the electrode for a few seconds after it’s dipped into the sample
solution and then hold it still. Wait for the reading to get fully stabilized ( appears and stays). Then
save the measurement by pressing

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7.2 Notes about ORP
ORP measurement does not require calibration. When the user is not sure about ORP electrode quality
or measuring value, use ORP 222 mV standard solution to test mV value and see whether ORP electrode
or meter works properly. Table-9 is the data of standard ORP solution for 222 mV.
Table-9
°C
10
15
20
25
30
35
38
40
mV
242
235
227
222
215
209
205
201
7.3 Clean and activate ORP electrode
After the electrode has been used over a long period of time, the platinum surface will get polluted which
causes inaccurate measurement and slow response. Please refer to the following methods to clean and
activate ORP electrode:
•In general, soaking the ORP electrode in 222 mV for 30 minutes will help activate the ORP sensor
and restore its accuracy.
•For inorganic pollutant, submerge the electrode in 0.1mol/L dilute hydrochloric acid for 30 minutes,
then wash it in distilled water, then submerge it in the soaking solution for 6 hours.
•For organic or lipid pollutant, clean the platinum surface with detergent, then wash it in distilled
water, then submerge it in the soaking solution for 6 hours.
•For heavily polluted platinum surface on which there is oxidation film, polish the platinum surface
with toothpaste, then wash it in distilled water, then submerge it in the 3M soaking solution for 6
hours.
7.4 ORP Parameter Setting
mV and ORP measurement parameter setting Table (Table (5-2))
Table (5-2)
Prompt mark
Parameter Setting Items
Code
Parameters
P1
Back light display time setting
bl
0-1-3-6 min
P2
Auto power off time setting
ac
0-10-20 min
7.4.1 Backlight display time setting (P1)
Press , the meter enters P1, see details in section 6.6.5
7.4.2 Auto power off time setting (P2)
Short press in P1 mode, the meter enters P2, see details in section 6.6.6

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8 Limited Warranty
We warrant this instrument to be free from defects in material and workmanship and agree to repair or
replace free of charge, at option of APERA INSTRUMENTS (Europe) GmbH, any malfunctioned or
damaged product attributable to responsibility of APERA INSTRUMENTS (Europe) GmbH for a period of
THREE YEARS (SIX MONTHS for the electrode) from the delivery.
This limited warranty does not cover any damages due to:
Transportation, storage, improper use, failure to follow the product instructions or to perform any
preventive maintenance, modifications, combination or use with any products, materials, processes,
systems or other matter not provided or authorized in writing by us, unauthorized repair, normal wear and
tear, or external causes such as accidents, abuse, or other actions or events beyond our reasonable
control.
APERA INSTRUMENTS (Europe) GmbH
Address: Wilhelm-Muthmann-Str.18
42329 Wuppertal, Germany
Tel: [phone]
Email: [e-mail]
Website: aperainst.de