Operation And Maintenance; Operation Theory; Flow Rate; Calibration (K-Factor) - Seametrics IP100 Series Instructions Manual

OPERATION AND MAINTANENCE

Operation Theory

In principle, an insertion flow sensor measures the velocity
of flow at one point in the pipe, and flow rate and total
can be inferred from this one point. Accuracy is decreased
by any factor which makes the flow at the measured point
unrepresentative of the entire flow stream. This includes
distorted flow patterns caused by upstream fittings too
close to the sensor. The worst offenders are fittings that
increase the flow on one side of the pipe, such as partially-
opened gate or butterfly valves. Fluid moving in a pipe
does not all flow at the same velocity. Toward the center
of the pipe, fluid moves faster than at the wall, and the
relationship between the two changes as overall flow rate
increases. This change in the "velocity profile" can result
in non-linearity, which means that the K-factor that is
correct for one flow rate may be incorrect for another. The
recommended depth settings have been carefully chosen
to minimize this source of error, and should be followed
carefully, especially in the smaller pipe sizes.

Flow Rate

These sensors are designed to operate at flow velocities
of 0.3 to 30 feet per second. (See chart for conversion to
gallons per minute.) If erratic readings are encountered at
low flows, check the chart to see if flow is below minimum
for the pipe size. The standard shaft and bearings should
have a long life at continuous high flow.
Calibration ("K-Factor")
In order to properly process pulses from the flow sensor,
a number must be entered into the control to which the
sensor is connected. This number, called the K-factor, is
the number of pulses the sensor puts out per unit of
fluid passing through the pipe. It is normally provided
for Seametrics sensors in pulses per gallon, and is given
on the chart "K-factors for Various Pipe Sizes."
numbers are based on extensive testing, which has shown
close agreement between different IP sensors in the same
installation. Typically, most K-factor error can be attributed
to installation variables, such as depth setting and fitting
configuration.
It is occasionally possible to field calibrate a sensor by
catching the fluid in a measured container and comparing
with the number of pulses recorded. (To record individual
pulses, set the K-factor on the control to 1.00.) This is
especially desirable if the installation has less than the
recommended length of straight pipe upstream of the
sensor.
Seametrics • 253.872.0284
All Seametrics flow sensors are repairable, and can be
returned to the factory or distributor for repair after a
Return Material Authorization (RMA) number has been
issued.

Rotor Replacement

Rotors are easily field-replaced. Shaft and rotor are a single
unit, and are not replaced separately. If replacement is due
only to normal shaft wear, bearing replacement is probably
not necessary. If the rotor has been damaged by impact,
the bearings should also be replaced. Rotor and bearings
can be ordered as a kit, Part No. 25902. Follow these steps:
1. Unscrew the threaded bearing housings to expose
the shaft ends. If bearings are being replaced, back
them completely out.
2. Remove the rotor. Put the new rotor in its place.
3. Thread in one bearing housing part way, then the
other. Take care to start the end of the shaft into
the bearing hole before tightening further.
4. Screw in bearing housings until they bottom.
Note: Do not use excessive force.
5. Check for free spin. Blowing lightly on the rotor
should result in it spinning rapidly and coasting to a
smooth stop.

Checking Signal

These
The flow sensor has only one moving part, the rotor. If
this is turning properly and there is no signal, the Hall-
effect sensor is not operating properly. To check the signal,
apply 12 Vdc regulated* power to the red (+) and black
(-) leads. Set a multimeter to voltage reading. Put the
positive multimeter lead on the red wire and the negative
lead on the white wire. Slowly turn the rotor. Voltage
reading should swing between +12 Volts and 0 Volts as
the rotor turns. If it does not, the Hall effect sensor is not
working properly. Checking for continuity is not a useful
test of these sensors.
*NOTE: An unregulated power supply can exceed max
voltage of micro-powered sensor pickup (gray cable) and
damage sensor.
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IP100/200 SERIES INSTRUCTIONS
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