EUTECH INSTRUMENTS WP PCD 650 Manuale delle Istruzioni Pagina 112
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Instruction Manual PCD 650
104
7. APPENDIX
7.1 Conductivity theory
Conductance is a quantity associated with the ability of primarily aqueous solutions
to carry an electrical current, I, between two metallic electrodes when a voltage E is
connected to them. Though water itself is a rather poor conductor of electricity, the
presence of ions in the water increases its conductance considerably, the current
being carried by the migration of the dissolved ions. This is a clear distinction from
the conduction of current through metal, which results from electron transport. The
conductance of a solution is proportional to and a good, though nonspecific indicator
of the concentration of ionic species present, as well as their charge and mobility. It
is intuitive that higher concentrations of ions in a liquid will conduct more current.
Conductance derives from Ohms law, E = IR, and is defined as the reciprocal of the
electrical resistance of a solution.
C = 1/R C is conductance (siemens) R is resistance (ohms)
One can combine Ohms law with the definition of conductance, and the resulting
relationship is:
C = I/E I is current (amps) E is potential (volts)
In practice, conductivity measurements involve determining the current through a
small portion of solution between two parallel electrode plates when an ac voltage is
applied. Conductivity values are related to the conductance (and thus the resistance)
of a solution by the physical dimensions - area and length - or the cell constant of the
measuring electrode. If the dimensions of the electrodes are such that the area of the
parallel plates is very large, it is reasonable that more ions can reside between the
plates, and more current can be measured. The physical distance between the
plates is also critical, as it affects the strength of the electric field between the plates.
If the plates are close and the electric field is strong, ions will reach the plates more
quickly than if the plates are far apart and the electric field is weak. By using cells
with defined plate areas and separation distances, it is possible to standardize or
specify conductance measurements.
Thus derives the term specific conductance or conductivity.
The relationship between conductance and specific conductivity is:
Specific Conductivity, S.C. = (Conductance) (cell constant, k) = siemens *
cm/cm
2
= siemens/cm
C is the Conductance (siemens) k is the cell constant, length/area or cm/cm
2
Since the basic unit of electrical resistance is the ohm, and conductance is the
reciprocal of resistance, the basic unit of conductance was originally designated a
“mho“- ohm spelled backwards - however, this term has been replace by the term
“siemen“. Conductivity measurements are reported as Siemens/cm, since the value
is measured between opposite faces of a cell of a known cubic configuration. With
most aqueous solutions, conductivity quantities are most frequently measured in
micro Siemens per cm (µS/cm) or mill Siemens per cm (mS/cm).
- WP PCD 650 1
- Preface 3
- Table of Contents 5
- 1. Getting Started 9
- 1.2 Display & Keypad 10
- 1.3 Inserting Batteries 12
- 1.4 Attaching Safety Belt 14
- 1.5 Connecting Peripherals 15
- 2. Measurement Mode 23
- Figure 17: Invalid key 24
- 2.2 Taking Measurement 25
- Figure 18: Under range 26
- Figure 19 : Hi alarm 26
- 2.3 Multi Display mode 30
- 2.4 pH Measurement Mode 31
- 2.5 mV Measurement Mode 32
- 2.6 Ion Measurement Mode 33
- 2.8 TDS Measurement Mode 35
- 3. Calibration Mode 47
- 3.2 Temperature Calibration 52
- 3.3 pH Calibration 54
- 3.4 mV Calibration 59
- 3.5 Ion Calibration 61
- 3.6 Conductivity Calibration 63
- 3.7 Resistivity Calibration 67
- 3.8 Salinity Calibration 69
- 3.9 TDS Calibration 71
- 4. Setup Mode 79
- 4.2 System Setup 83
- 4.3 pH Setup 90
- 4.5 Ion Setup 93
- 4.6 Conductivity Setup 94
- 4.7 TDS Setup 96
- 4.8 Salinity Setup 98
- 4.9 Resistivity Setup 100
- % - DO Saturation Setup 102
- Instruction Manual PCD 650 104
- 4.12 Temperature Setup 106
- 5. Technical Specifications 107
- Salinity 108
- Resistivity 108
- PCD 650 108
- TDS at TDS factor 1.000 108
- 6. Accessories 110
- 7. APPENDIX 112
- 7.4 Dissolved Oxygen Probe 115
- Figure 93: Use Tool to take 117
- 8. General Information 118
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