Principle Of Operation - Hach EC1000 Instruction Manual

1.8 Principle of Operation

Note: The electrolyte
pump is not used with the
self-pressurized Industrial
Process pH Electrode with
self-pressurized
electrolyte, Cat. No.
48276-00. See Section 1.6
Industrial Process pH
Electrode.
Figure 5 System Components
The EC1000 Process pH/ORP System consists of a combination pH or ORP electrode, a
controller, and a reference electrolyte pump (see Figure 5 on page 23). The electrode
consists of a pH or ORP measuring half cell and a double junction reference half cell,
which establish a potential characteristic of the sample. This potential is converted to a
proportional current by a built in preamplifier in order to stabilize the signal for long
distance transmission to the controller. Included in the electrode is a temperature sensor
whose signal also is stabilized and sent to the controller to allow for temperature
compensation or temperature correction of the pH/ORP measurement. Separate from the
controller and electrode is a reference electrolyte pump that supplies fresh electrolyte to
the reference half cell. The pumped electrolyte maintains an open reference junction
through a capillary outlet to produce a stable and constant reference potential.
As the electrode measures the pH (or mV) of the water source, a signal is transmitted to
the controller. If the pH (or mV) is outside the setpoint range, the controller can transmit
a current output signal to a reagent pump (or valve) that adds reagent to a mixing tank. See
Figure 6 on page 24 for details. As the reagent is added to the water, the value of the pH
(or redox potential) is adjusted to fall within the setpoint range. Refer to SECTION 4, PID
CONTROL, for a detailed discussion of this process.
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