Calibration Guidelines
Calibration Guidelines
Calibration Guidelines
pH Meter
Introduction:
You can calibrate the pH meter for three pH levels, but pH7 is most important. If you
have limited time and/or resources, it’s OK if you just test for pH7 only. If you are testing
all three solutions, test pH7 first, and then pH4 and pH10 in any order following. It is best
to calibrate the pH meter(s) up to 24-48 hours before the water monitoring event, or less.
Record your calibration on the provided sheet for pH7 only, not pH4 or pH10. Check for
a “BAT” symbol flashing on the pH meter, which indicates low batteries. Be sure to
record low batteries on the calibration sheet, and notify a San Diego Coastkeeper water
monitoring staff member. Be aware that the meters will automatically turn off after 3-5
min. as a battery saving precaution, so don’t leave the meter sitting for more than 5 min.
or it will turn off.
Materials:
pH meters you wish to calibrate
Calibration solutions pH4, pH7 & pH10
Three 80mL beakers – fill with enough calibration solution to submerge the instrument’s
electrodes
Step-by-Step Instructions:
1) Pour the pH7 calibration solution into an 80mL beaker. You want to be able to
submerge the entire electrode, so be sure to pour enough to make this possible,
but not so much that there is a lot of excess so we don’t waste calibration solution.
2) Rinse the electrode with DI H2O and gently shake off excess H2O.
3) Insert the pH meter into the pH7 calibration solution, deep enough so the entire
electrode is submerged.
4) Swirl the electrode for a few seconds, and then leave still in the solution for up to
2 minutes.
5) Wait until the pH value stops fluxuating and settles on one value; record that
value on the calibration sheet under “current reading.”
6) Now, you are ready to calibrate. Press and release the “CAL” button. On the
pHTestr3 instruments, the value will start to blink, however on the pHTestr30
instruments the value does not blink. Once settled, press the “HOLD” button.
7) The value will settle at the calibrated value, which should take no longer than 30
seconds. [The pH meter will automatically settle at the pH value closest to the
pre-calibration value. Ex: If the pre-calibration value was 7.25, the pH meter
should calibrate to 7.00, or something very close to that. – is this correct? Or is it
] The value should then read “7.00.”
8) Record the value after calibration on the provided sheet under “reading after
calibration,” even if it’s not exactly 7.00. You only have to record the pre and post
calibration values for the pH7 calibration, not the subsequent pH4 and pH10
Clean-up:
You can safely pour all pH calibration solutions down the sink drain; they are not
hazardous.
Return the pH calibration solutions and DI H2O squeeze bottle(s) to the appropriate
cabinet for storage.
Wash all beakers and dry on the drying rack; return to the appropriate cabinet once dry
for storage.
Make sure all calibrated pH meters are turned off and put in the correct monitoring
box(es), or stored all together and clearly dated and labeled “calibrated.”
Make sure you’ve filled out all the fields on the calibration sheet and return to the
clipboard on the wall to the right of the sink.
Conductivity Meter
Materials:
Conductivity meters you wish to calibrate
Traceable Conductivity Calibration Standard Solution (1,413)
One 80mL beaker – fill with enough calibration solution to submerge the instrument’s
electrodes
De-ionized “DI” H2O for rinsing electrodes
Step-by-Step Instructions:
1) Rinse electrode with DI H2O and gently shake off excess H2O, you can gently
towel off the excess water if needed – just don’t towel off the electrodes.
2) Turn on the instrument and insert the Conductivity meter into the calibration
solution, deep enough so the entire electrode is submerged.
3) Swirl the electrode for a few seconds, and then leave still in the solution for up to
2 minutes.
4) Wait until the conductivity value stops fluxuating and settles on one value; record
that value on the calibration sheet under “reading before calibration.”
5) Hold down the “CAL” button for a few seconds and release. It will immediately
start blinking “1,413” a few times, and then will settle on the actual calibrated
value.
6) Record the value after calibration on the provided sheet under “reading after
calibration,” it should be exactly “1,413”.
7) Now that the conductivity meter is calibrated, you need to complete a control
chart. To do this, you will record the conductivity level of the same solution (use
the same calibration solution you calibrated the conductivity meter with) seven
times. Be sure to rinse the electrode with DI H2O in between each reading. You
can test in the same solution because you are testing the same instrument. Once
this procedure is complete, plot your results on the provided charts (conductivity
values on the Y axis, reading number on the X axis). This will help us see if the
conductivity meter is taking accurate readings, or if it needs to be replaced. If the
readings are going up and down slightly each time (a horizontal zigzag), that is
optimal. If the readings are going consistently up or down from readings 1 to 7,
the conductivity meter needs to be re-calibrated. If the problem persists, you
should not use the conductivity meter, as it probably needs to be replaced.
8) A 5% swing on either side of 1,413 is generally bad and should be recorded in the
notes section of the calibration sheet. However, you will likely see a swing greater
than that on the control chart (around 10-15%), as the conductivity meters are
highly variable. Still make a note of it on the calibration sheet.
9) Once calibration is complete, store the electrode damp. To do this, you do not
need to rinse the electrode with DI H2O, simply take out of the calibration
Clean-up:
You can safely pour the Traceable Conductivity Calibration Standard Solution down the
sink drain; it is not hazardous.
Return the Traceable Conductivity Calibration Standard Solution and DI H2O squeeze
bottle(s) to the appropriate cabinet for storage.
Wash all beakers and dry on the drying rack; return to the appropriate cabinet once dry
for storage.
Make sure all calibrated conductivity meters are put in the correct monitoring box(es), or
stored all together and clearly dated and labeled “calibrated.”
Make sure you’ve filled out all the fields on the calibration sheet and return to the
clipboard on the wall to the right of the sink.
Materials:
DO meters you wish to calibrate
New membranes (only if you need to change the membranes – should only be performed
by a San Diego Coastkeeper water monitoring staff member)
Step-by-Step Instructions:
1) Make sure the DO meter is reading “O2,” not “mg/L.” This will allow you to
calibrate using air.
2) Without attaching the probe, turn the meter on. It should read “0.”
3) Plug in the probe and take off the cap. Be very careful to remove the cap gently,
easing off from the bottom of the cap. Never pull from the top or twist, which are
the motions that tend to break the membrane and/or crack the probe tip. Leave
probe open to the air in the room for a few minutes (can prop up on something to
keep the DO meter stable) until the value settles on one value.
4) Once the value is stable, press the “Ox Cal” button and release to calibrate.
5) You do not need to complete a control chart, or fill out the calibration sheet. You
do need to check off and date the calibration event on the checklist provided to
record that the calibration was completed.
6) Once the calibration is complete, turn off the DO meter. Be sure to change the
reading units to “mg/L” to set the DO meter to test water during the upcoming
water monitoring event.
7) Unplug probe before storing.
Clean-up:
Make sure all calibrated DO meters are put in the correct monitoring box(es), or stored all
together and clearly dated and labeled “calibrated.”
Make sure you’ve completed the calibration checklist and return to the clipboard on the
wall to the right of the sink.