Emerson Process Management 3081 pH/ORP instruction manual Section Glossary, Term Definition

MODEL 3081 pH/ORP	SECTION 16.0
	GLOSSARY

SECTION 16.0

GLOSSARY

TERM	DEFINITION
Acid	When dissolved in water acids increase the hydrogen ion concentration. Pure
	water at 25°C contains 1 x 10-7moles per liter of hydrogen ions (H+) and an equal
	concentration of hydroxide ions (OH-). An acid increases the hydrogen ion con-
	centration above the value found in pure water and decreases the hydroxide ion
	concentration. However, the product of the hydroxide and hydrogen concentra-
	tions remains constant.
Activity	Physical and chemical measurements made in real solutions are usually different
	from the values predicted from the behavior in ideal solutions. Activity is a way of
	accounting for the discrepancy. For ions in solution ideal behavior occurs at infi-
	nite dilution. Infinite dilution means the solution contains so few ions that they
	behave independently of one another. As the concentration of the ions increase,
	they start to interact and the properties of the solution begin to deviate from the
	ideal. The ratio of the true value to the ideal value at a given concentration is the
	activity coefficient. The product of the activity coefficient and the concentration is
	the activity. For electrolytes, the activity is always less than the concentration.
Alkalai metal	The alkalai metals are lithium, sodium, potassium, and cesium. They form ions
	having unit positive charge. Ion exchange reactions involving alkalai metal ions
	cause certain types of glass to develop electrical potentials in the presence of
	hydrogen ions.
AMS	AMS is an acronym for Asset Management Solutions. AMS is software running in
	Windows 95 that allows the user, sitting at a computer, to view process measure-
	ments, program transmitters, and review maintenance and performance records.
Balco RTD	The sensing element in a Balco RTD is an alloy containing 70% nickel and 30%
	iron. Balco RTDs are identified by their resistance at 25°C. The resistance
	changes about +0.45% per °C.
Base	When dissolved in water bases decrease the hydrogen ion concentration. Pure
	water at 25°C contains 1 x 10-7moles per liter of hydrogen ions (H+) and an equal
	concentration of hydroxide ions (OH-). A base decreases the hydrogen ion con-
	centration below the value found in pure water and increases the hydroxide ion
	concentration. However, the product of the hydroxide and hydrogen concentra-
	tions remains constant. Alkalai is another word for base.
Buffer (calibration)	A calibration buffer is a solution having accurately known pH. Calibration buffers
	have a nominal pH, which is the pH at 25°C. Changing the temperature changes
	the pH value of a buffer. Buffers define the pH scale and are used to calibrate the
	response of pH measurement cells.
Buffer	The term buffer generally refers to a solution that resists changes in pH upon dilu-
	tion or the addition of small amount of a strong acid or base.
Calibration	Chemical sensors are transducers. They produce a signal related to concentra-
	tion or to a physical property. Calibration is the process of assigning known con-
	centrations or known physical values to the sensor signal. Because the relation-
	ship between sensor output and physical or chemical property is often linear, only
	one or two calibration points are needed.

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