2. If oscillations are modest and over a period of less than one minute, this can be dampened out by
lengthening the residual fi lter period time (consult factory or your authorized Hydro Instruments dealer
to change the fi lter time).
3. If oscillations are modest and over a longer period of time, performed coinciding test kit samples to
determine if the readings are correct or not.
Slow reaction to residual changes
This may be caused by coating of the cell electrodes, dirt or debris in the cell or by excessively long fi lter
times.
Residual reading is unreliable at low residual levels
1. This may be the result of attempting to monitor a residual level at the very low end of the ordered
range. For example, if a particular analyzer is ordered and set-up for a measurement range of 0 – 5.0
mg/l and the actual application involves measuring for residuals of 0.1 or 0.2 mg/l, the accuracy of the
measurement will suff er. If the normal measurement range is less than 25% of the ordered range,
contact Hydro Instruments or an authorized distributor for guidance on resetting the range of the
analyzer.
2. This may also be caused by coating of the cell electrodes, dirt or debris in the cell or by improper
residual calibration.
NOTE: It is important to note that the residual span calibration should never be performed with a very
low residual, as compared to the measurement range for which the analyzer was provided. The span
calibration should be performed with a residual value of at least 25% of the ordered range. Ideally,
the span calibration should be performed with a residual value of 50% or more of the ordered range.
If the normal measurement range is less than 25% of the ordered range, contact Hydro Instruments
or an authorized distributor for guidance on resetting the range of the analyzer.
Temperature
Temperature reading is not correct
1. Independently test sample water temperature and verify the temperature.
2. If the displayed temperature is not correct, recalibrate the temperature.
3. If the displayed temperature is extremely high or extremely low, the thermistor has either lost
connection to the circuit board or has failed, requiring replacement. This is a 10K Ohm resistor and
replacements are available from Hydro Instruments.
Thermistor is damaged or missing
1. Replace thermistor.
2. The temperature compensation mode can be set to “Manual” to allow for continued analyzer
operation until the thermistor is replaced.
pH
pH reading does not match independent pH meter measurement
1. Recalibrate pH.
2. Recalibration can be performed at a single point (“grab cal”) or at two points using known pH buff ers.
3. If the pH being displayed is dramatically incorrect or fl uctuating drastically and cannot be corrected
through a two-point calibration, check all pH cable connections as well as the cable
connector
to
the probe. If all connections are verifi ed and the problem cannot be corrected through recalibration,
replace the pH electrode (Hydro part number PHE-250).
4. If the raw pH sensor mV values are outside the acceptable ranges listed in the table on Figure 9 of
this manual, then replace the pH probe.
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