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