Accumet AP74 User manual

OPERATING INSTRUCTIONS
accumet®13636AP74A
Portable Waterproof
Dissolved Oxygen
Meter
Printed 1/02
IP
67

2
Table of Contents
1. Introduction............................................................................................4
2. Display and keypad functions .............................................................5-6
2.1 Display...................................................................................................................................5
2.2 Keypad...................................................................................................................................6
3. Preparation..........................................................................................7-8
3.1 Inserting the batteries..........................................................................................................7
3.2 Connecting the probe...........................................................................................................8
4. Calibration.........................................................................................9-14
4.1 Preparing the meter for calibration...................................................................................9
4.2 Dissolved oxygen calibration in % saturation..........................................................10-11
4.3 Dissolved oxygen calibration in mg/l (ppm) mode ...............................................12-13
4.4 Temperature calibration....................................................................................................14
5. Measurement...................................................................................15-18
5.1 Taking DO readings......................................................................................................15-16
5.2 Taking pressure/salinity compensated DO measurements...................................17-18
6. Hold function........................................................................................19
7. Memory functions............................................................................20-21
7.1 Memory input.....................................................................................................................20
7.2 Memory recall.....................................................................................................................21
8. Advanced setup functions...............................................................23-39
Advanced setup mode overview......................................................................................23-25
mg/l (ppm) measurement mode overview...................................................................24
% saturation measurement mode overview .................................................................25
8.1 Program Clr: Memory clear..............................................................................................26
8.2 Program dPr: Dissolved oxygen parameters............................................................27-28
Pressure adjustment mode................................................................................................27
Salinity adjustment mode .................................................................................................28
8.3 Program OFS: Offset for % saturation measurement ...................................................29
8.4 Program CAL: Previous calibration information..........................................................30

3
8.5 Program ELE: Electrode properties.................................................................................31
View probe slope................................................................................................................31
View % saturation offset....................................................................................................31
View 100% saturation mV value......................................................................................31
View 0% saturation mV value..........................................................................................31
8.6 Program COF: Unit configuration..............................................................................32-34
Ready indicator and auto endpoint function.................................................................32
Selecting mg/l or pm units...............................................................................................33
Selecting °C or °F temperature readout..........................................................................34
8.7 Program LCd: Adjusting LCD brightness......................................................................35
8.8 Program CLO: Setting the real-time clock ................................................................36-37
8.9 Program rST:Resetting to factory default settings .......................................................38
9. Probe care and maintenance...........................................................39-42
9.1 Probe care ............................................................................................................................39
9.2 Membrane replacement ...............................................................................................40-41
9.3 Electrolyte solution ............................................................................................................41
10. Troubleshooting..................................................................................42
11. Error Messages....................................................................................43
12. Specifications......................................................................................44
14. Appendix 1: Meter theory ..................................................................45
15, Appendix 2: Pressure vs. Altitude table.............................................46
16. Appendix 3: Factory default settings.................................................47

4
1. Introduction
Thank you for selecting an accumet AP74 Dissolved Oxygen meter. This portable
meter is a microprocessor-based instrument that measures dissolved oxygen and
temperature. It’s completely waterproof—and it floats! Your meter has many
user-friendly features, all of which are accessible through the membrane keypad.
Your meter includes a dissolved oxygen/temperature probe, electrolyte solution,
and batteries. Please read this manual thoroughly before operating your meter.

5
2. Display and Keypad Functions
Display
The LCD has a primary and secondary display.
• The primary display shows the measured dissolved oxygen reading.
• The secondary display shows the temperature of the reading.
The display also shows error messages, keypad functions and program functions.
2.1
Primary display
5.
6.
Secondary display
3.
2.
17.
18.
16.
10.
14. 13. 12.
8.
1.
15.
4.
11.
7.
1. SETup mode indicator
2. MEASurement mode
indicator
3. CALibration indicator
4. MEMory recall mode
indicator
5. % saturation indicator
6. Salinity input indicator
7. Oxygen solubility
indicators
8. Temperature
indicators
9.Automatic Temperature
Compensation
indicator
10. Clock indicator
11. ERRor indicator
12. MEMory location
indicator
13. Low battery indicator
14. Probe indicator
15. Calibration data
indicator
16. Function ON/OFF
indicator
17. HOLD indicator
18. READY indicator
9.

6
Keypad
The large membrane keypad makes the instrument easy to use. Each button, when
pressed, has a corresponding graphic indicator on the LCD.
ON/OFF............Powers and shuts off the meter.
HOLD ..............Freezes the measured reading. To activate, press HOLD while in
measurement mode. To release, press HOLD again.
NOTE: When auto endpoint feature is switched on, it automatically
holds reading after 5 seconds of stability. The HOLD indicator
appears on the display. Press HOLD to release auto endpoint feature.
MODE..............Selects the measurement parameter. Press MODE to toggle between
DO % saturation; DO mg/l (ppm); and date/time. In DO calibration
mode, press MODE to access temperature calibration.
NOTE: To switch between mg/l and ppm modes, see page 33.
CAL/MEAS......Toggles user between Calibration and Measurement mode.
• If you were in DO % saturation mode, press CAL/MEAS to enter
DO % saturation calibration mode.
• If you were in DO mg/l (ppm) mode, press CAL/MEAS
to enter DO mg/l (ppm) calibration mode.
NOTE: Temperature calibration is available from DO calibration
mode; see page 14 for directions.
In advanced set-up mode: Press CAL/MEAS to return to main menu
from sub menus. Press CAL/MEAS again to return to measurement
mode from main menu.
ENTER ............Press to confirm values in Calibration mode and to confirm
selections in Setup mode.
▲▼..........Press in Setup mode to scroll through subgroups. Also lets you
increment/decrement the values in the mg/l and temperature
calibration modes.
..........................MI/MR work in the
measurement mode. MI
(memory input) stores the
measured value into memory.
MR (memory recall) recalls
the sets of values stored in
the memory.
SETUP..............Press to enter SETUP
mode. SETUP mode lets
you customize meter
preferences and defaults,
and view calibration and
probe data.
..........................LIGHT Press to activate
backlit display.
MI MR
2.2

7
Battery
compartment
Remove these
two screws to
access battery
compartment
3. Preparation
Inserting the Batteries
Four AAA batteries are included with your meter.
1. Use a Phillips screwdriver to remove the two screws holding the battery cover.
See figure below.
2. Lift off battery cover to expose batteries.
3. Insert batteries. Follow the diagram inside the cover for correct polarity.
4. Replace the battery cover into its original position. Screw cover back into place.
3.1

8
Connecting the probe
Your meter includes a dissolved oxygen/temperature probe. The probe cable has a
notched 6-pin connector to attach the probe to the meter.
NOTE: Do not substitute other probes.
NOTE: Keep connector dry and clean. Do not touch connector with soiled hands.
To connect the probe:
1. Line up the notch and 6 pins on the top of the meter with the holes in the probe
connector. Push down and turn the locking ring to lock into place.
See figure below.
2. To remove probe, turn the locking ring on the probe connector.
Pull probe away from the meter.
CAUTION: Do not pull on the probe cord or the probe wires might disconnect.
3.2
locking ring
top view of 6-pin
connector

9
4. Calibration
Probe guard
Preparing the meter for calibration
Before calibrating your meter, make sure to rinse the
probe well with de-ionized water or rinse solution.
NOTE: Do not let membrane surface of the probe
touch any other surface. The probe guard
(the piece with holes fitted over the end of
the probe) protects the membrane; make sure
this is always attached to the probe while it is
in use.
You can calibrate for dissolved oxygen in either
% saturation or mg/l (ppm). All new calibrations
automatically override existing calibration data.
Before calibration
Before starting calibration, make sure you are in the
correct measurement mode. When you switch on the
meter, the meter starts up in the units last used (either
mg/l, ppm, % air saturation, or clock). For example, if
you shut the meter off in “mg/l” units, the meter will
read “mg/l” units when you switch the meter on.
NOTE: Most users will calibrate to 100% saturation
even when working in mg/l. When calibrat-
ing the meter in mg/l mode, you can make
fine adjustments, typically to a midrange
value between 10 and 100%. If you are
calibrating to a midrange value, you need
to set the 100% saturation value first.
4.1

To calibrate 100 % saturation:
1. Rinse the probe well with deionized
rinse water or rinse solution. For best
accuracy, wrap the end of the probe
in a damp cloth. Do not touch the
membrane.
2. Press the MODE key to select the
% saturation mode.
See figure
3. Press the CAL key. The CAL indicator
will appear above the primary display.
The primary display shows the current
value of the measurement and the
secondary display will show 100.0
(see NOTE above).
See figure
4. Hold the probe in the air (or in damp
cloth). Wait for the reading to stabilize.
If the Ready indicator feature is enabled,
it will appear when the reading is stable
(see page 32).
5. Press the ENTER key. The meter auto-
matically calibrates to 100.0% air satura-
tion and returns to Measurement mode.
See figure
10
4.2
A
A
B
C
B
C
Dissolved Oxygen calibration in percent saturation
You can calibrate this meter quickly and easily in air. The exact calibration value
depends on barometric pressure. The meter is set to a factory default of 760 mm Hg,
which results in a calibration value of 100% saturation in air.
NOTE: If the barometric pressure setting has been changed from 760 mm Hg, the
calibration value in air will automatically adjust to a value other than 100%.
The adjusted value will be correct for the new barometric pressure setting.
• See page 27 to change the pressure setting.
• See Appendix 2 on page 46 for a chart of adjusted % saturation values.
Notes
The reading in the primary display in step 3 must read at 50% or above for the
calibration to work correctly. Whenever an error occurs during calibration, the
ERR indicator appears in the lower left hand corner of the display.
You can offset your % DO calibration: see page 29 for directions.

To calibrate 0 % saturation:
1. Rinse the probe well with deionized
rinse water or rinse solution. Do not
touch the membrane.
2. Press the MODE key to select the
% saturation mode.
See figure
2. Place the probe in zero oxygen
solution. Stir the probe gently to
homogenize the sample. Make sure
that the sample is continuously flowing
past the membrane sensor.
3. Press the CAL key. The CAL indicator
will appear above the primary display.
The primary display shows the current
value of the measurement and the
secondary display will show 0.0.
See figure
4. Wait for the reading to stabilize. If the
Ready indicator feature is enabled, it
will appear when the reading is stable
(see page 32).
5. Press the ENTER key. The meter auto-
matically calibrates to 0.0% saturation
and returns to Measurement mode.
See figure
Notes
The reading in the primary display in step
3 must read at 10% or under for the calibra-
tion to work correctly. Whenever an error
occurs during calibration, the ERR indicator
appears in the lower left hand corner of the
display.
You can offset your % DO calibration: see
page 29 for directions.
11
D
D
E
E
F
F

12
To calibrate in mg/l (ppm) mode:
1. Calibrate 100% saturation per section 4.1.
2. Rinse the probe well with deionized
rinse water or rinse solution. Wipe the
outside of the probe carefully (do not
touch the membrane).
3. Dip the probe into a sample of known
oxygen concentration. Wait for the
reading to stabilize. If the Ready
indicator feature is enabled, it will appear
when the reading is stable (see page 32).
NOTE: The sample must continuously flow
past the membrane for accurate
readings. A stirrer can keep the
solution agitated; order a magnetic
stirrer on page 47.
4. Press the MODE key to select the
mg/l (ppm) mode.
See figure
5. Press the CAL key. The CAL indicator
will appear above the primary display.
The primary display shows the current
value of the measurement and the sec-
ondary display shows the temperature.
See figure
6. Press the ▲and ▼keys to adjust
the reading.
7. Press the ENTER key. The meter
automatically calibrates to the
value you entered and returns
to Measurement mode.
See figure
4.3
A
A
B
C
C
B
Dissolved Oxygen calibration in mg/l (ppm) mode
Calibrating the meter to 100 % in saturation mode will also calibrate the mg/l mode
at the value in mg/l corresponding to 100% saturation. This should produce
acceptable results in most applications.
This meter also lets you make a calibration adjustment in mg/l (ppm) mode
without affecting your % saturation calibration.
To select between mg/l and ppm units, see page 33.

13
Notes on mg/l (ppm) mode calibration
During mg/l (ppm) calibration, the meter adjusts to the
barometric pressure value that is programmed into the
meter. It also adjusts to the salinity value that is pro-
grammed into the meter.
You can change the barometric pressure value and
salinity value in the mg/l (ppm) Set Up mode (see
pages 27-28 for directions).
Whenever an error occurs during calibration, the ERR
indicator appears in the lower left hand corner of the
display.

14
Temperature Calibration
The built-in temperature sensor included in the probe is factory calibrated.
Calibrate your sensor only if you suspect sensor drift that may have occurred
over a long period of time or if you have a replacement probe.
1. Switch the meter on. Press MODE to
select mg/l (ppm) Measurement mode.
2. Press the CAL/MEAS key to enter
mg/l (ppm) calibration mode. The
CAL indicator will appear above the
primary display.
See figure
3. While in mg/l (ppm) calibration mode,
press the MODE key to enter tempera-
ture calibration mode. The primary
display shows the last set temperature
reading and the secondary display
shows you the factory default
temperature value.
See figure
4. Compare the primary display reading
to a NIST-traceable thermometer or
another thermometer known to be
accurate.
5. Press the ▲or ▼keys to adjust
the primary display reading to agree
with your temperature standard.
See figure
6. Press the ENTER key to confirm
temperature calibration and return to
Measurement mode.
Notes
To exit from Temperature Calibration mode
without confirming calibration, DO NOT
press ENTER in step 6. Press CAL/MEAS
instead.
Temperature calibration is restricted to
±5°C from the factory default value
displayed during calibration (shown in the
secondary display).
A
B
C
4.4
A
B
C

15
5. Measurement
Taking DO readings
During measurement, the probe can be:
• fully immersed in the solution
• partially immersed in the solution
Do not allow the probe’s membrane surface to touch any-
thing! The probe guard (the piece with holes fitted over the
end of the probe) protects the membrane; you should leave
this piece attached to the probe at all times.
IMPORTANT: since the DO probe consumes oxygen
from the sample, the sample must constantly flow past the
membrane to achieve more accurate readings. You can use
a stirrer to accomplish this.
To take measurements:
1. Rinse the probe well with deionized
rinse water or rinse solution.
2. Select the appropriate measurement
mode. Press the MODE key to toggle
between modes:
• %saturation.
• mg/l (ppm)**,
• date/time clock
3. Dip the probe into the sample. Stir the
probe gently to homogenize the sample.
Make sure that the sample is continuously
flowing past the membrane sensor.
4. Note the reading on the display. If the
READY indicator is switched on, it will
appear when the reading is stable.
See figure
5. Press the key to activate the backlit
LCD. This helps you read measurements
in dimly lit areas. The backlit display
automatically turns off 20 seconds after
releasing the key to conserve batteries.
5.1
A
A
Probe guard
**To select between mg/l and ppm units, see page 33.
The ATC indicator should appear in the lower right hand corner of the display.
If it does not, this indicates an error.
CONTINUED ON NEXT PAGE

16
Taking measurements with READY indicator selected on
If the READY indicator has been activated, the READY annunciator lights when
the reading is stable. Switch the READY indicator on or off in the Set up program—
see page 32 for directions.
Taking measurements with the auto endpoint feature selected on
When a reading is stable for more than 5 seconds, the auto endpoint feature will
automatically “hold” the reading. The “hold” indicator appears on the left side of
the display. Press the HOLD key to release the reading. Switch the Auto endpoint
feature on or off in the Set up program—see page 32 for directions.

17
Taking pressure/salinity compensated DO measurements
If necessary, you can adjust the pressure and salinity values of your measurements
in the Set Up mode. The DO meter will automatically compensate for salinity and
pressure based on the values entered in the setup functions. The meter is factory set
at 760 mm Hg (101.3 Pascals) pressure adjustment and a factor of 0.0 salinity adjust-
ment. See Appendix 2 on page 46 for a “Pressure vs Altitude” table.
Pressure adjustment
1. Press the SETUP key to enter Set Up
mode.
2. Press the ▲key once. The upper display
shows “dPr”.
See figure
3. Press the ENTER key until the upper
display shows a number and the lower
display shows “Hg” or “PA”.
4. Use the ▲and ▼keys to enter the
barometric pressure. The upper display
will show the value you have entered.
See figure
5. Press ENTER to confirm pressure value.
6. Press CAL/MEAS to return to
Measurement mode, or continue
with step 4 on page 18 to make a salinity
adjustment [available from mg/l (ppm)
mode only].
5.2
A
B
A
B

18
Salinity adjustment
NOTE: this mode appears in ppm (mg/l)
measurement mode only.
1. Press the Mode key to select mg/l (ppm)
mode.
2. Press the SETUP key to enter Set Up
mode.
3. Press the ▲key until the upper display
shows “dPr”.
See figure
4. Press the ENTER key until the upper
display shows a number and the lower
display shows “SAL”.
5. Use the ▲and ▼keys to enter the
salinity of your solution in ppt. The
upper display will show the value you
have entered.
See figure
6. Press the ENTER key to confirm value.
7. Press CAL/MEAS to return to
Measurement mode.
A
B
A
B

19
This feature lets you freeze the dissolved
oxygen and temperature readings for a
delayed observation. HOLD can be used
any time when in MEAS mode.
1. To hold a measurement, press the
HOLD key while in measurement
mode. "HOLD" will appear on the
display.
See figure
2. To release the held value, press HOLD
again. Continue to take measurements.
NOTE: This meter shuts off automatically
after 20 minutes of nonuse.
If the meter is shut off either
automatically or manually, the
HOLD value will be lost. For
longer storage, use the memory
functions (see pages 20-21).
NOTE: This meter has an auto endpoint
feature. When this feature is
switched on, the display will
automatically “hold” a reading
that has been stable for more than
5 seconds. The “hold” indicator
appears. Press the HOLD key to
release the reading. To switch on or
off the auto endpoint feature, see
page 32.
A
A
6. HOLD function