YSI 5200 - Manual (Page 111)

YSI Incorporated 109 5200 Recirculating System Monitor
10. (5562 Probe only) Activate the 2-point pH calibration protocol from the 5200 display and
recalibrate the instrument using the two buffers as described in Section 6.2.4 pH Calibration.
11. Rinse the probe with water and place in the calibration/storage cap containing about 1/8 inch (3
mm) of water. Make sure that the dissolved oxygen sensor is not immersed in the water.
12. Wait about 5 minutes for temperature equilibration and then record the dissolved oxygen reading
in percent air saturation as shown on the 5200 display.
13. If the dissolved oxygen readings show minimal drift (within about 5 % of the correct value) and
are stable, proceed with Step #13. If excessive drift is noted or the readings are jumpy, replace the
membrane cap as described in Section 4.6 Membrane Cap Installation, then proceed with Step
#13 after allowing a 10-15 minute break-in period before calibrating.
14. Activate the DO % calibration protocol from the 5200 display and recalibrate the instrument to
the current altitude. See Section 6.2.2 Dissolved Oxygen Calibration.
15. Replace the probe in the sample stream and continue monitoring.
NOTE: The procedure does not include quantitative data taken with regard to either the
temperature or conductivity sensors. The temperature sensor only fails in very rare circumstances
and, when it does, the temperature readings will seem unreasonable for the current conditions. In
the unlikely event that the temperature sensor shows unusual and/or jumpy readings, it will need
to be checked by authorized service personnel. No user service is possible. For the conductivity
sensor, drift is usually minimal except as caused by build-up of debris in the cell. Once this is
cleaned out as described in Step 5 above, the sensor almost always yields accurate readings again
with no recalibration needed. However, if you wish to check your conductivity calibration, place
the probe in a known standard being sure that the top vent hole is completely covered. If
significant drift has occurred, recalibrate the sensor as described in Section 6.2.3 Conductivity
Calibration.
16. Test all control and alarm relays for proper operation.
11.3.1 Alternative Quality Assurance Protocol (quick check and
adjustment)
An alternative, complementary type of quality assurance program to that described above for the sensors
can be carried out by comparing the current dissolved oxygen and pH readings shown on the 5200 display
with those taken by recently-calibrated hand held instruments. For dissolved oxygen, the probe of a
handheld DO instrument similar to the YSI 550 can be placed in the stream near the 5200 Probe and the
reading recorded. If a comparison of the readings from the recently-calibrated DO meter and the 5200
indicates a drift, the 5200 system can be recalibrated to reflect the DO meter reading. Note, however, that
this comparison should only be used in a reset of the calibration if the 5200 Probe has been cleaned of all
algae and other debris prior to the determination. If a gross variation is observed between the two
instruments (> 1 mg/L), it is usually a sign that maintenance is required on the 5200 DO sensor.
For pH, a similar field calibration adjustment can be made using a YSI 60 or 63 field pH meter.
Alternatively, a sample of the stream can be taken to the laboratory for evaluation of the true pH. After
this value is determined, you should immediately return to the deployment site and, leaving the 5200
probe in the water, perform a single point pH calibration inputting the laboratory pH as the calibration
value.
It is important to remember, however, that this “adjustment” of DO and pH values to those determined by
recently calibrated single parameter instruments should only be used to compensate for minor drifts. It is
not a substitute for the detailed quality assurance procedure outlined above which confirms proper sensor
function and which should always be performed on a regular basis.