ORP-200 01/08
CARE, MAINTENANCE & TECHNIQUES
As with all ORP and pH meters, the ORP-200 requires proper maintenance to ensure a healthy lifespan
for the meter. With proper care, the sensor will be good for approximately 12 months. Sensor lifespans
vary, and replacement ORP-200 sensors can be purchased from your HM Digital distributor.
General techniques:
1. Do not store the unit in high temperature or direct sunlight.
2. Store the meter upright (standing on the cap, so that you can read the text).
3. Never touch the sensor! Skin oils may adversely affect the reading. If you do touch the sensor,
clean immediately with distilled water or a pH 7 buffer solution (see cleaning instructions).
4. Always immediately replace the cap when the meter is not in use. The ORP-200 cap contains a
small wetted sponge or cotton ball to ensure that the gel within the glass sensor does not dry up.
NOTE – A tightened cap will ensure a longer lifespan for your sensor!
5. It is normal for salt deposits to form on the outside of the cap or rim of the cap. This is from the
bottling solution from within the cap, having dried up. If salt deposits appear, simply wipe off with a soft
tissue and rubbing alcohol.
6. Using the ORP-200 in high temperature liquid, such as hot coffee, will shorten the lifespan of the
sensor. If testing in hot liquid is essential, be sure to not
keep the meter in the hot liquid very long.
(Room temperature coffee will not adversely affect the sensor.)
7. After repeated usage in high TDS liquids, it is advised to clean the sensor to prevent residue build-
up.
8. If testing liquids other than water, always be sure to rinse the sensor with distilled water or a ph 7
buffer solution afterwards.
9. If testing two samples over a wide range (e.g., -400 mV and 700 mV), make sure to rinse the sensor
in distilled water or a pH 7 buffer solution between and after tests. Avoid keeping the sensor in very
high or low ORP liquid for extended periods. High or low ORP values may take longer to register.
10. For optimum performance, it is best to use the meter at least once per month.
For best measurement accuracy:
1. Though it is not necessary, the ORP-200 will be more accurate if calibrated before each use. This is
the case with all digital ORP and pH meters.
2. Clean with distilled water or a pH 7 buffer solution after each use, even if checking the same sample.
3. If an air bubble is lodged in the sensor, dip the meter in distilled water and stir. Remove the meter
and shake excess water off.
4. If the sensor is scratched, it must be replaced.
5. If the readings seem to slow down and continue to get slower, or the meter seems to have become
unresponsive or sluggish, you may need to change the batteries or replace the sensor. Lifespans of
sensors are limited. Lifespans vary depending upon usage. It is normal for a sensor to wear out.
FOR ADVANCED USERS ONLY: If the meter is continuously used to check widely varying mV levels
and is also continuously recalibrated at different levels, performance may be affected. If you find your
meter is not be working at optimum performance, press and hold the ‘TEMP/CAL’ button. Once ‘CAL’ is
flashing on the screen, press and hold both the ‘TEMP/CAL’ and ‘HOLD’ buttons at the same time for
two seconds. This will reset the calibration. It is then necessary to recalibrate the meter (see the
Calibration chapter for more information).
HOUSING AND SCREEN DESCRIPTION
Housing
1. Lanyard hook
2. Battery compartment
3. LCD display
4. Button panel
5. Power button
6. Calibration mode, temperature mode,
calibration-up button
7. Hold, calibration-down button
8. Sensor gasket ring
9. Detachable sensor (electrode)
LCD Display
1. Low battery indicator
2. ORP measurement (mV)
3. Temperature measurement
4. Celsius/Fahrenheit mode
5. Hold mode
BEFORE YOU START!
1. The meter is shipped with the cap on tight to ensure proper condition of the electrode, which must
remain wet. You will notice that there is liquid in the cap (a 4 pH KCl buffer solution). Be careful not
to spill it. To remove the cap, hold the meter and twist off.
2. For new meters, allow a longer response time for measurement readings. The response time of your
meter will quicken with usage. For your first few tests, lightly swirl the meter in the water/solution 3
times and allow the meter to sit while adjusting to the reading.
3. If you need to test the ORP of low conductivity water (below 50 µS), you should do so only after
using the meter a few times in an ORP buffer solution or higher conductivity water.
4. Never touch the electrode or reference tube. Be sure not to touch the glass electrode or reference
tube to the side of a glass or beaker.
5. Always make sure that the cap is on tight after usage.
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