MODEL 100 FLO-SENSOR
FREQUENTLY ASKED QUESTIONS
1. Since the Model 100 Flo-Sensor uses the Pelton Turbine Wheel
Principle, how in general, is its behavior when comparing its operation to either a ball
and tube rotameter or mass flow sensor?
Turbine Wheel gas flow sensors behave very closely in operation to that of ball and
tube rotameters in many ways, but, it , of course, provides a linear D.C. output voltage
proportional to flow rate. Unlike thermal mass flow sensors, Model 100, due to its design,
has no zero drift problems.
2. Linearity is quoted at + 3% full scale. At what %
of full scale does the maximum non-linearity occur and is this % position the same for all
ranges of flow sensors?
+ 3% full scale linearity is a safe tolerance for production
of flow sensors. (see figures III thru V). There will be
no absolute pattern, but many units shipped are quite linear. Others fall near
maximum limits. We offer a $200.00 calibration service for individuals who desire
the actual data. This price is subject to change without notice and excludes
3. Are the Flo-Sensors sensitive to mounting orientation?
Yes, the flow sensors, like conventional ball and tube flow meters, are sensitive to
mounting orientation and have been tested at factory in horizontal position. Units
can be recalibrated vertically or on their sides but calibration data will differ.
Refer to INSTALLATION information on page 4 of X-100 instruction manual. Models
100-3 and 100-4 only operate horizontally.
4. Do you recommend using an in-line filter before the sensor?
Yes, an in-line filter is quite beneficial and will insure longer life and minimize
fouling us sensor. We suggest 7 or 10 micron filtering. Also, when operating
with most gases, sensor should be kept slightly warmer than the gases (within limit of its
maximum operating temperature) to prevent moisture from condensing so that water droplets
get into sensor. This can stop the operation of flow sensor until all liquid
droplets have been baked out of sensor.
5. Quoted maximum operating pressures is 40psi 20º C. Is
this absolute or gauge pressure? Can unit be operated above 40psi? Is sensor
sensitive to line pressure in reading flow rate? What is the typical pressure drop
40psi is 40psig. We do not suggest operation at pressures in excess of this
value. Although in proof pressure tests, failure of a plastic tube fitting at
380psig was first failure noted (test was at 25° C.). It is perfectly okay to
operate sensor at 30psig all the time but sensor is sensitive to line pressure. See
enclosed technical data, figure I. Pressure drop across sensor
varies with flow rate. Model 100-3 pressure drop is 20 inches of water at 100ml/min
of dry air flow. Models 100-6 through 8 have 2 inches of water pressure drop at
their rated flows.
6. Below the minimum specified flow rate (say less than 20 ml/min
for the 100-3 Flo-Sensor) does the turbine wheel actually stop rotating or is it just that
the output voltage is unreliable or non-linear? Do you intend to supply a flow
sensor capable of measuring gas flows below 20ml/min?
For 100-3, the turbine wheel typically stops rotating at about 8ml/min. Between
8ml/min and 20ml/min, the flow sensor would actually send out at D.C. voltage signal but
it would be somewhat lower in voltage than the straight line voltage vs. flow rate curve
indicates. Here again, since these units are mass produced, we cannot give you any
specific curve since every unit would be a little different. We do not currently
anticipate producing a gas flow sensor for measurement of gases below 20ml/min. See figures III through V.
7. Can the Flo-Sensors be damaged by flow rates much higher than
their maximum rated flow rates?
Flow sensors can be continuously operated up to 6 VDC without damage. This is
about 20% higher than rated flow rate. Units can be subjected to 3 to 4 times normal
maximum rated flow without damage so long as the unit is only momentarily hit with such a
high flow rate. Life expectancy is increased 9 times longer when operating at 1/3
8. Can the Flo-Sensors be used for corrosive gases such as SO2,
NO2, NO, or H2S?
Yes, units are operating on many gases including SO2, NO2 and H2S.
9. What is the expected life of the sensors? What components
are most likely to fail first?
Guaranteed life is one year. We do not yet have sufficient field experience to
tell us expected life. Bearings and turbine wheel shaft are the only items we expect
will fail. See question 7.
10. You specify two types of tube fittings, Acetal and Kynar.
When would your use one fitting rather than the other? You specify two types of
"O" rings, silicone and citon, when would you use one type of "O" ring
rather than the other?
See enclosures pertaining to "O" rings and fittings, table
I & II.
11. What tubing diameter do you suggest for connecting to the
All low flow range sensors are designed for operation up to and including 1
liter/minute using 1/8" tubing. At flow rates in excess of 1 liter/minute, we
go the fittings designed to accept 1/4" tubing. (above 20L/min. use 3/8" O.D.
tubing.) Above 50L/min. use 1/2" O.D. tubing.
12. What is the output impedance of the 0-5 VDC output voltage?
Output impedance of flow sensor is virtually 0 ohms, but if a load lower than 2500
ohms is applied across output, the internal circuitry begins to artificially add impedance
up to 300 ohms to prevent a short circuit malfunction. So we suggest that customer
not draw more than 1 milliampere from our flow sensor to insure best operation.
This would mean sensor would drive into a load of at least 5000 ohms.
13. When operating Flo-Sensor on gases other than air, does the
Yes, like a conventional ball and tube rotameter, model 100 Flo-Sensor needs to be
calibrated on the gas type that will be flowing through it. See curve enclosed
showing calibration adjustments for gases other than air. Customer should specify
gas type when ordering. Otherwise all Flo-Sensors are routinely calibrated using
air. (Figure II)
14. Temperature sensitivity is how in relation to increasing
temperature or decreasing temperature?
Increasing temperature causes a rise in output voltage at rate of 0.2%/C. or less
without any change in actual gas flow rate. Like wise decreasing temperature causes
a decrease in output voltage at rate of 0.2%/C. or less without any change in actual gas
flow rate. A step change in temperature will not cause an instantaneous error to
occur in output signal. Time constant for error change to occur due to step change
in temperature is approximately 15-30 minutes.
15. Can Flo-Sensors operate at voltages other than the specified
12.5VDC + 2VDC?
Yes, 100B models operate at 3-6 VDC. Special units can be ordered to operate
from 9 VDC to in excess of 16 VDC. Contact factory for details.
16. Can you provide a pulse output?
Yes, we can furnish an unbuffered 0-500 pps output that corresponds to flow rate where
500 pps is full scale flow output.
17. Since turbine wheel shaft and/or sapphire bearings are subject
to wear and will eventually fail, what is the policy for repair and replacement of these
Units shipped to us freight prepaid will be repaired at no charge if within our one
year warranty. If out of warranty, a $75.00 repair charge will apply as of January
1, 1991. Repair charges for out of warranty repairs are subject to change without
notice. This charge of $75.00 includes retest of unit on air to insure its proper
operation. Shipment will normally be U.P.S. and freight charges will be added to
invoice charges. A simple change out of a saddle assembly which takes 5 minutes
includes bearings, turbine wheel and shaft and is simple to install. Current cost is
$57.50. Customer can install these saddle assemblies.
18. Would you show us typical flow rate versus voltage output
curves for the various gas flow sensors?
Three curves are enclosed as representative. Note, however, that each flow
sensor shipped could deviate within specification limits from these representative flow
rate versus voltage curves. If it is desired to have the actual calibration data for
a particular flow sensor, this can be furnished at added cost. Contact factory for
details and specify gas that will be used. Actual pressure inside housing that unit
will experience during operation
19. What is response time constant of flo-sensor?
Typically 8 - 10 seconds for 0-63% of final value. Approx. 30
seconds for 98% of final value..