Liquid Temperature - ABB MAG-X 3000 Series Instruction Manual

INSTRUCTION MANUAL 10DX3111A&G Sizes 14 - 24 Inches
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., 36 k x 2/10
and,
typical electrode diameter is 0.375" (0.952 cm)
For example, assuming the measured ac electrode resistance (full pipe and zero flow) is 192,000
ohms and electrode diameter is 0.952 cm, then
σ
=
(0.192 - 0.072) x 0.952
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. ABB Automation Field Engineers
are equipped to determine the conductivities of special liquids at the user's site as an engineering
service.

4.2.1.2 Liquid Temperature

Having established the minimum liquid conductivity requirements for a given application, any liquid
which exhibits equal or higher conductivity may be metered without concern for any system compen-
sating adjustments. However, due regard for the effect of the liquid conductivity versus temperature
should be considered.
Most liquids exhibit a positive temperature coefficient of conductivity. It is possible for certain
marginal liquids to become sufficiently non-conductive at lower temperatures so as to hamper
accurate metering; whereas, the same liquid at higher or normal environmental temperatures may be
metered with optimum results. The possibility of an adverse temperature conductivity characteristic
should be investigated before attempting to meter such a liquid. Liquid or ambient temperatures are
also limited by the meter materials specification.
Other normal effects of temperature, such as influence upon liquid viscosity and density, the size of
the metering area, and the flux density of the magnetic field, have negligible or no effect upon
metering accuracy.
4-4
1
- 0.072) x Electrode Dia, in cm
1
= 8.75 µs/cm
6