Hach 2100AN Instrument Manual page 56

SECTION 5,
continued
5.2.2.4 Selecting FILL TIME
5.2.2.5 Selecting MEASUREMENT TIME
Note: A minimum measurement
time of 15 seconds is required.
5.2.2.6 Using
STATIC
Note: Check to ensure the proper
wavelength filter module is installed
before beginning measurement (see
SECTION 10 on page 85).
In Dynamic mode, the flow valve remains open at the end of the programmed fill
time. Measurement is made on the flowing (dynamic) sample stream as it moves
through the Flow Cell.
The fill time is the time interval that the Flow Valve remains open so that sample
flows through the system before measurements are taken. Fill time is
programmable from 0 seconds to 99 minutes and 99 seconds. A fill time setting of
0 seconds causes the instrument to begin measurement with no delay. Select the
fill time duration to account for filling the system and also to thoroughly purge the
system of all previous sample. The total volume of the Flow-Cell System
(excluding the 350-mL Inlet Reservoir), from the discharge of the Inlet Reservoir
to the outlet of the Flow-Cell, is approximately 30 mL. Flow rate through the
system is approximately 250 mL/min.
Hach Company suggests a minimum volume of 120 mL (fill time = 30 seconds) to
purge the system of previous sample. This volume purges the system
approximately 4 times. A shorter fill time may be appropriate when making
repeated measurements of the same sample.
When measuring several samples of varying turbidity, measure the samples in
order of the cleanest (lowest turbidity) to the dirtiest (highest turbidity) to
minimize carry-over from one sample to the next.
Measurement time is the time interval the instrument actively measures the sample
turbidity. A measurement is completed approximately once per second, and the
display is updated.
Measurement time is programmable from 0 to 99 minutes and 99 seconds. The last
displayed value is held in the display and the results of measurement are
automatically transmitted to the built-in printer (and/or through the RS232 output
to an external printer or computer if connected) at the end of the programmed
measurement time. The instrument continues to hold the last value until the
key is pressed to exit the
measurement portion of the cycle without repeating the fill time.
Selection of a 0 measurement time provides continuous measurement that may be
desirable when operating in the dynamic measurement mode; the instrument
continues sample measurement until the
mode. Selection of a 0 measurement time for static measurements is of limited
value when using the static measurement mode because particles in the sample
may settle over time. Therefore, the resulting measurements may not be
representative of original sample.
Measurement Mode
In the static mode the Flow Valve opens, the cell fills, sample continues to flow
for the programmed fill time interval, and then the Flow Valve closes. The
turbidimeter makes measurements during the programmed measurement time.
The final reading is held in the display, and the result of the measurement is
transmitted to the built-in printer (and/or through the RS232 output to an external
printer or computer if connected).
mode, or the
FLOW ENTER
FLOW
56
key is pressed to repeat the
key is pressed to exit the Flow
FLOW