YSI 5200A - Manual (Page 92)

YSI 5200A
183
YSI 5200A
182
Maintenance
Certain routine maintenance must be performed to keep the instrument operat-
ing properly. Maintenance includes servicing sensors and output devices. The
quality of input data is dependent on three factors:
- General maintenance at the physical deployment site of the probe as-
sembly.
- A well-defined quality assurance program that is carried out on a regu-
lar basis to ensure that the sensors are performing properly.
- Proper periodic calibration and maintenance of the specific sensors.
This chapter is designed to help in these important areas by providing mainte-
nance tips, help in implementing a quality assurance protocol, and suggested
service methods and intervals for the sensors.
Probe Maintenance at the Deployment Site
Algae and Debris
A common problem with regard to the overall probe assembly deployment site is
fouling from algae (and other debris). Algae will inevitably collect on any object
immersed in water and, unless periodically removed, it can inhibit the sensor’s
measurement. Once algae build-up occurs on the sensors and/or probe guard, it
isolates the sensor’s environment from the sample stream. To avoid or minimize
this problem, it is necessary to periodically remove the algae and biofouling from
the probe guard and sensors.
Minimizing the Effect of Algae and Debris
The collection of algae on the probe and the frequency of cleaning can be mini-
mized by deploying the probe so that it is angled with (rather than against) the
current of the stream. This deployment method will maximize the chances of the
algae being swept free from the probe rather than collecting on it.
Remember that no matter what precautions are taken, debris will still collect on
the probe and the fouling will have to be removed by periodic cleaning. Cleaning
will be easier if the probe mounting method allows for easy removal and replace-
ment of the probe. A little extra time spent implementing a good probe mount
and using the optional probe mounting kits will save time in subsequent probe
cleanings.
The frequency in which you will have to remove fouling from the probe varies
with the type of water being monitored and the physical deployment of the probe.
The need for cleaning can usually be ascertained by visual inspection. You can
do no harm by excess cleaning so it is best to remove and clean the probe if any
significant fouling is suspected.
Maintenance
Calibration Checks
The sensors are of high quality and should exhibit excellent performance in ex-
cess of the warranty period, see page 237. However, the dissolved oxygen, pH,
ORP, and conductivity sensors will inevitably show some drift during deploy-
ment due to natural chemical changes to the reagents in the probes, physical
changes of the electrodes, and/or minor fouling of the sensor surfaces. Incon-
sistent (fluctuating or noisy) sensor readings (especially for the conductivity and
dissolved oxygen sensors) signal the need for maintenance procedures specific to
those sensors. With these factors in mind, it is imperative that you establish and
carry out regular quality checks of the sensor readings to ensure that sensor val-
ues are being reported accurately and within specifications. The quality checks
can help determine when sensor maintenance or calibration is required.
Recommended Quality Assurance Protocol
This product has been designed and tested to provide trouble free service. How-
ever, as with all microprocessor based products, there is potential for failure which
could cause loss of control functions. Proper QC (Quality Control) procedures can
reduce the potential for failure.
It is recommended that you carry out the following quality assurance program
weekly during the initial use of the 5200A system. After several weeks of this
program, you should be able to ascertain if this frequency is appropriate for your
application. If only minimal drift is observed, then the frequency of quality checks
can be decreased. The procedure is relatively simple and should take only about
20 minutes to complete.
1. Take the following items to the deployment site:
- bucket for clean water to rinse sensors
- small brush supplied with the conductivity sensor
- calibration/storage cup supplied with the probe/cable assembly
- solution and/or secondary instrument to verify values displayed by sen-
sor. See Calibration starting on 82“Calibration Menu” on page 74.
- latex gloves
2. Disable any system control and/or alarm relays that may become active as
a result of value(s) generated during the validation process. For example
if a pH system is configured to energize a control low relay at ≤ 7.5 and
validation is being made by placing the sensor in pH 4 buffer, the control
low relay will energize and may adversely affect the pH water system based
on the pH 4 buffer value.
3. Place the 5200A in Service Hold mode. See pages 128 and 169 for
Service Hold information.
4. Remove the probe from the sample stream.
Maintenance