Answer / rajesh

pH is a measure of the acidity or basicity of a solution. pH
is a potentiometric measurement where the electrode used
produces an electrical signal which the pH meter converts to
a pH reading. The signal produced and measured is a voltage
and since voltage is a potential difference, two potentials
are needed to make a measurement:

a) The sensing electrode provides a potential proportional
to the logarithm of the hydrogen ion activity in the sample.
b) The reference electrode ideally provides a stable and
consistent potential independent of the activity of the sample.

The potential difference between the reference and sensing
electrode is measured by the meter and converted into a pH
value.

All pH sensors consist of a measuring glass electrode and
reference electrode. A combination electrode is an electrode
which contains both the reference and measuring electrode in
the one body. The reference electrode provides a constant
potential regardless of the composition of the solution it
is placed in. The voltage difference between the reference
and measuring electrodes is a function of the pH value of a
solution.

Calibration is done using pH Buffers. Most modern pH meters
are supplied with the facility for automatic buffer
recognition. The manufacturer will have programmed in a pH
versus temperature profile into memory for a specific type
of buffer. If a different buffer to that specified by the
manufacturer is used for calibration this will result in
calibration errors. For proper calibration, buffer solutions
of carefully selected accuracy and pH range are required.
The calibration should be performed using two buffers whose
values bracket the expected value of the samples being
measured. In practice many pH meters are equipped with auto
buffer recognition - this requires the use of the buffer
values specified by the meter manufacturer.

Can a pneumatic control valve work without positioner?

4 Answers   SMC,

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HI friends.I am Surya a BTech in Electronics and Instrumentation Engineering.I am going to appear Relince Industries Ltd all India writen test very soon. so plz help me by sendind the probable questions about my subject.My mail ID is surya.barik@gmail.com.

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is any standard angle for thermowell mounting for horizontal and vertical pipe lines?

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In control valve there are two type of valve seat we can use metal to metal seat & soft seat.On this valve seat i have following doubt. 1)I have never seen practically the internal assembly of valve so my doubt is that basically weather the seat is soft seat or metal its basic MOC is same as valve body(SS or CS) only in soft seat we are using PTFE ring & place on valve seat & in metal this PTFE ring is not threr am i correct??????? 2)what are the common general rule for using metal to metal seat & soft seat,means its depend on process parameter like liquid,gas, steam & on valve leakage class.

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1 Answers   Schneider,

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what is diff between sensors and transducers.explain with ex?

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0 Answers   IOCL, ITC Infotech,

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What is Hysteresis mean in Instrument?

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How to make position transmitter feedback reverse i.e at valve close i want 20ma output and at full open 4ma.for the NELES positioner,model:ND8261/TS1.

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why pneumatic control signal output is use 0.2 to 1 kg/cm2

3 Answers   Jindal,

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