Arkon Channelmag - Manual (Page 23)

23
ChannelMag
Section 4 Maintenance
4.1 Cleaning
4.2 Zero Span Checking
4.3 Effect of Moisture
4.4 Effect of a
4.5 Effect of One Sensor
Of Two Inoperative
Under typical operating conditions the ChannelMag sensor requires no maintenance. Due to the
uniquely high signal to media noise ratio, the affects of such coatings as algae, sewage grease,
calcium carbonate, iron oxides or similar coatings have no affect on published accuracy. As such
cleaning of coatings is normally unnecessary.
Should there be silt or similar non-fluidic build up, the upper surface of the ChannelMag sensor
must be cleaned. However, with the ramp construction the upper surface it is highly unlikely to
become covered with silt or similar.
When the CM2 is in a recess in the bed of the channel, it is recommended to have its upper surface
slightly above the bed of the channel, but not more than ½” (12mm). This avoids excessive silt or
similar build up, as well as avoiding too much turbulence due to the step from the bed to the upper
surface. If more than ½” (12mm) is required, then the step to the upper surface should have suitable
grouting at an angle of less than 15 º.
Ingression
With the ChannelMag sensor connected to the 4411e transmitter, check for zero and span in
accordance with the 4411e Instruction Manual. This confirms the electrical function of the
transmitter.
Note: Bad grounding will not affect the electrical zero and span test.
Grounded Electrode
The exciter coils of the ChannelMag sensor should be checked at the transmitter end. Remove from
terminals 4, 5 and shield 6. There should be a minimum 10Meg Ohms (typically > 20Meg Ohms)
between 4 and 6 and 5 and 6 respectively. If there is less than 10Meg Ohms, moisture has probably
leaked into the sensor and /or the cable, resulting in signal instability. The cable should be inspected
for damage or dried out or cut away where any moisture may be. If the sensor has leakage it must
be returned to ARKON or approved representative.
To check if there is electrical ground at the electrodes, the cable ends 24 and shield and 25 and
shield respectively are removed from the terminals of the transmitter. The resistances should
approximately the same between each and between 100k Ohms to 5 M Ohms. If any electrode is
grounded the signal will be at approximately ¾ of the normal signal. Remove anything highly
conductive between the appropriate electrode and ground.
If there are two ChannelMag sensors used as one flow system in a channel, the electrodes and coils
are wired in parallel. Should one sensor coil become defective, then the system will continue to
operate, but there will be a small inaccuracy due to operating with only one sensor. If this is
unacceptable a replacement sensor can be installed at a convenient time. The erroneous sensor can
be determined by checking as above in the junction box.