Faults easily encountered in the measurement of pH value by hand-held acidity meter
Hand-held acidity meter is a commonly used instrument and equipment, mainly used to precisely measure the pH value of liquid medium, coupled with the corresponding ion selective electrode can also measure the MV value of ion electrode potential, widely used in industry, agriculture, scientific research, environmental protection, etc. field.
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One: Handheld acidity meter potentiometer and circuit troubleshooting
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The main part of the hand-held acidity meter is a precision potentiometer. Due to long-term soaking in acid and alkali and its high precision, when a fault occurs, first check whether there is a problem with the matching electrode of the instrument.
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Detection method: If there is a spare electrode, you can replace the electrode for inspection. If there is no spare electrode, you can check whether there is a problem with the circuit of the hand-held acidity meter.
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If the hand-held acidity meter is short-circuited, the pH value will be displayed as 7, and the millivolt value will be displayed as 0. In addition, the zeroing of the instrument is normal and the positioning output is also normal. It can be preliminarily judged that the circuit system of the instrument is basically working normally. The indication error of the instrument can be measured with a DC potentiometer. If the pH value displayed by the handheld acidity meter is 14 and the millivolt value corresponding to A is about 421, it means that the indication error of the instrument basically meets the requirements.
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Two: Common faults and solutions in the use of hand-held acidity meters:
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1. When the power is turned on, the indicator light is off
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(1) If the instrument has voltage output, check whether the indicator light is burnt out;
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(2) If the instrument has no voltage output, check whether the fuse ALL is new;
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(3) If the fuse is not blown, check whether the transformer of the instrument is burnt out due to a partial short circuit in the circuit.
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2. When the power is turned on, the indicator on the meter head of the instrument is unstable or the pointer is not positioned
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(1) Open the panel of the instrument to check whether the meter head is stuck, and observe whether there is any foreign matter on the coil;
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(2) Check whether the instrument casing is grounded.
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3. When the power is not turned on, the indicator on the meter head swings sharply; open the panel of the instrument to check whether the parallel resistance welding at the input end behind the meter head is firm.
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4. After the hand-held acidity meter is powered on, the displayed number is unstable or drifts
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(1) Check whether the connectors of the instrument are firm;
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(2) Check whether the input and output voltage of the instrument are stable;
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(3) Check whether the circuit board of the instrument is corroded;
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(4) Check whether the operational amplifier in the amplifier circuit of the instrument is burnt out.
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5. The output indication of the hand-held acidity meter is inaccurate; the detection method is incorrect or the temperature and slope adjustment points are incorrect.
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6. Two kinds of standard solutions cannot be used for mutual positioning; check whether the standard signal generator is inaccurate.
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7. The hand-held acidity meter can work normally when it is directly input, but the indication value is out of tolerance when it is connected in series with high resistance.
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(1) Check whether the filter capacitor of the instrument is broken down;
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(2) Check whether the input resistance of the field effect bamboo of the instrument is low;
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(3) Check whether the circuit board of the instrument is damp or corroded.
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8. After the handheld acidity meter is powered on, the numbers displayed are missing strokes
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(1) The connector of the instrument is not in good contact;
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(2) The digital display of the instrument is damaged.
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9. The temperature, slope or correction adjustment knob on the hand-held acidity meter panel is out of order; check whether the potentiometer connected to the out-of-function knob is damaged.
