109
DEFINITIONS
DEVIATION
Same as proportional band, but expressed in units of the
controlled magnitude (e .g . 1pH, 50 mV) .
EEPROM
Electrically Erasable Programmable Read-only Memory
(permanent memory) .
FAIL SAFE ALARM
Signaling of the alarm by de-energizing the alarm relay
instead of energizing it . That protects against power failures
and interruptions of the alarm relay external wires .
GLP
Good Laboratory Practice .
HYSTERESIS
Interval that must be passed over by the controlled mag-
nitude in the opposite direction after having activated a
relay, before deactivating it, in order to avoid uninterrupted
activation/deactivation of the relay .
IN-LINE CLEANING
Automatic procedure to stop control, clean the electrode
and then activate control again .
NIST
National Institute of Standards and Technology .
PID
Proportional Integrative Derivative control .
POTENTIAL MATCHING PIN
Pin for connection of the potential matching (or
grounding) steel bar, which must be immersed into the
measured fluid, and is used together with a differential input
to avoid damage of the reference electrode due to ground
loop current .
PROPORTIONAL BAND Interval, measured in percentage of the input range, where
the proportional action spans from 0 to 100 % .
PWM
Pulse Width Modulation .
RAM
Random Access Memory (non-permanent memory) .
RTC
Real Time Clock .
SETPOINT
Value at which the measurement needs to be controlled .
SOLUTION COMPENSATION
Technique for compensating the differences on the
pH of the solution under measurement when its temperature
varies .
THRESHOLD
Value above/below which a control or alarm relay is acti-
vated or deactivated .
TRIGGER
An event or command that acts like a mechanical trigger
in initiating a process .
WATCHDOG
Mechanism for issuing a reset of the device in case it gets
stuck .
