Operating Characteristics; Liquid Variables - ABB 3000 Series Instruction Manual

4.2 Operating Characteristics

4.2.1 Liquid Variables

4.2.1.1 Liquid Conductivity
The Flowmeter requires a liquid conductivity of 5 microsiemens per centimeter or higher for opera-
tion. This minimum liquid conductivity requirement is effected by the length of the signal interconnec-
tion cable to the signal converter. The nominal maximum transmission distance is limited to 50 feet
(15 m), however, a 100 foot (30 m) cable length can be accommodated with a minimum conductivity
of 20 µS.
The conductivity of a given liquid,
condition, as follows:
1) Remove the converter housing cover. Disconnect the electrode signal interconnection
leads from terminals "1" and "2" of the signal converter. (These leads should be identified
so that they will be properly reconnected.)
2) Measure the resistance between signal leads "1" and "2" with an AC ohmmeter.
Do not use a DC ohmmeter for this measurement as polarization
The conductivity of the process liquid (in microsiemens/cm) may be determined from the electrode
AC resistance measurement (in megohms) by substitution of values in the following equation.
σ
=
(R
ac
where,
0.072 is the electrode barrier resistance in megohms; i.e.,
36000 x 2
6
10
For example, assuming the measured AC electrode resistance (full pipe and zero flow) is 192,000
ohms and electrode diameter is 7.92 mm (0.792 cm), then
σ
=
(0.192 - 0.072) x 0.635
This is above the threshold for specified measurement accuracy for the particular liquid, meter size
and signal converter combination. Liquid conductivities at the operating temperature may also be
determined from standard reference works for many pure liquids. Field Engineers are equipped to
determine the conductivities of special liquids at the user's site.
10DS3111A INSTRUCTION MANUAL
σ
, may be determined experimentally under a filled meter
CAUTION
effects will produce completely erroneous data.
1
- 0.072) x Electrode Dia, in cm
1
= 13.16 µS/cm
4-3