trouble shooting

  • I am getting a negative flow rate, why is this happening?

    Please check connections – see below:


    Reversing connections US V1 and US V2 will result in a negative flow reading

  • How do I check calibration of flow on flow transmitter?


    On 4-20 mA output terminals, fit link between 12V and Iout+ connectors. Set Multi-meter to read mA and measure between Iout- and 0V terminals. In Mainstream Communicator, select Outputs / 4-20mA / Calibration. You can now calibrate the outputs using the meter and also test their linearity.

  • Can the Mainstream analogue output be configured to provide 4mA at maximum reverse flow (-4,000 m3/hr), 12mA at zero flow and 20mA at maximum forward flow (+4,000 m3/hr) ?

    Using your example (2), set 4 mA to correspond to -4,000 m3/hr and 20 mA to correspond to 4,000 m3/hr.  At zero flow (half way between the two set points) the output will be half way between 4 mA and 20 mA, i.e. 12 mA.

  • Can a relay be set to change state depending on flow direction? eg 'on' for forward flow and 'off' for reverse flow?

    Using the switch outputs set the switch to change state at zero flow.

  • How does the Mainstream flow totaliser work?

    Inside the Mainstream, flow quantities are calculated in litres.  Mainstream uses 32-bit floating point numbers for the internal calculations.  This gives a number range from 10^-63 to 10^63.  Precision is 1 part in 16 million  – better than seven decimal digits.

    The minimum quantity that can be represented is 10^-60 cubic millimetres – much smaller than the volume of a water molecule.  The maximum quantity that can be represented is 10^60 cubic metres – larger than the volume of the solar system.

    The totalizer never automatically resets (wraps round) to zero.  It only needs to be reset for operational reasons, or to limit the accumulation of errors.

  • Can you measure the flow in a pipe with a 15° slope and how does it affect the Zone of Inspection?

    If you increase the 15° elevation angle, for example by placing a wedge underneath the probe, the Zone of Inspection can penetrate further into the flow but you decrease the probe scale factor and increase the sensitivity to fluid motion transverse to the channel axis, e.g. swirl.  In the limit, if you direct the ultrasound beam across the flow you should only detect this transverse motion and be unable to detect the mean flow velocity.  The elevation angle and beam width were chosen to give the best compromise.

    If the flow velocity is above the maximum 5 m/s that Mainstream can measure you need to change the configuration of the flow.  A partial blockage downstream of the velocity probe is sometimes effective, or a horizontal section followed by a weir.  The pipe diameter (or maximum flow rate) determines whether alterations to the flow structure can be cost effective.

  • What are the limits in size for measuring the level and channel section?

    Mainstream has worked with up to 2 metres diameter pipes in waste water.  We do not normally recommend operating the Mainstream flowmeter in pipes greater than 2.5 to 3 metres in diameter and channels greater than 2.5 to 3 metres wide.  This is because the flow information collected by the velocity probe typically extends up to about 1.5 metres into the flow.

  • Can Mainstream work in channels greater than 3 metres wide?

    It is possible to use the Mainstream flowmeter in larger channels in much the same way that an insertion probe is used to indicate the flow in a large pipe.  In a channel, you use velocity measurements from the Mainstream taken at a sequence of points across the section to establish the velocity profile.  Averaging these gives the mean velocity.  You then place the velocity probe in the location where it is to be installed, typically looking across the channel, and record the indicated velocity.  Set the probe scale factor to 0.736 x mean velocity / indicated velocity and the Mainstream reads the correct flow rate.

    Clearly, this only works well when the velocity profile is stable – prismatic channel with no obstructions or flow into or out of the channel near to the measurement site – and when the range of level is limited.  However, within these limitations the Mainstream will give useful flow information.

  • Is there any maximum height offset in an installation, and, if you make this offset does it influence the accuracy of measurement? This is for conditions where we do not want to install the sensor on the bottom of the channel, however how does the sensor measure the velocity of liquid that is lower than the level of the sensor position?

    The velocity probe will only measure the velocity in the ‘zone of inspection’ so you should position the probe to get best coverage of the flow. If you do not want to install the probe very close to the bottom of the pipe/channel it is usually because of debris and settled solids.  The measurement is better if you keep above this level.  You lose information from below the probe but you get good information from the rest of the flow.

  • Is it possible to draw the section profile in AutoCAD and insert it to the Mainstream software as DWG format? Which formats are acceptable for importing to the Mainstream software and how? (They said that in some cases they can’t specify the exact size of the channels by Mainstream software.)

    We have looked at making a .DFX interface but it will not appear from some time yet.  If you cannot input the pipe/channel section using the graphics tools you can specify and load this information as a level-area table.  Within Communicator you need to configure the units to be used.

  • Is it possible entering the channels size diameter directly as numerical values to the software and how?

    Not directly, but you can produce a spreadsheet that will calculate a level-area table when you input the key dimensions.  Create a .CSV file in Excel with one column for Level and one for Area.  Calculate an area for a specified level and then copy that formula through other specified levels.  Go to the Channel Section Editor and import the .CSV file.

  • How can you take the data process as a graph?

    If you retrieve the logged data into a spreadsheet e.g. Excel, you can use the graphics tools to produce time histories.  One useful trick is to plot level against velocity.  This can be used to show that you have stable hydraulic conditions – the channels is not being blocked/unblocked.

  • What’s your guidance for best usage and maintain this equipment in healthy conditions?

    This depends very much on the application.  If you notice that the signal quality is falling this suggests that the probe may be becoming covered in debris and needs cleaning.  You can do this in place with a brush or similar.  You can usually learn about the needs of an application and set up a routine – perhaps every three or four weeks – sometimes more frequently – sometimes less.

  • What can harm the unit and the sensors?

    The sensors can be subject to physical damage by debris carried by the flow.  In this case you can sometimes mount the sensor pointing downstream and fit a cover for protection.

    Very rapid changes in temperature (thermal shocks) are bad for the sensor.  Avoid this if at all possible.

    You should always keep water out of the system unit.  If possible mount the system unit out of direct sunlight as prolonged high temperatures can damage the LCD.

  • Is there an option for damping the Mainstream?

    You can go to VELOCITY, CONFIGURATION and then select Noise Suppression where there is a drop down menu to select from Small to Very Large.  Ensure that Histogram Averaging is enabled. OK then Apply.

    Don’t change the sampling interval – that controls the velocity range.

  • Can the sampling frequency vary according to the flow level?

    Recording frequency cannot vary according to the flow or level.  Simply set the recording rate to the highest required and discard any unwanted data.

  • How frequently does the totaliser update?

    The flow is totalised in the hour quantity.  Every hour, on the hour, the hour quantity is added to the total quantity and the hour quantity is then cleared.

    The engineering units only affects the quantity displays.  The actual quantities are unchanged.  If gallons are selected it will display gallons and total gallons.  If cubic metres are selected it will display cubic metres.

  • What is the reason that Mainstream uses a totaliser indication hourly instead of instantaneously. This feature is very useful when you need to do test or to know partial inventory during any time.

    Mainstream use 32 bit floating point numbers.  To prevent round off errors it is necessary to use two totalisers.  So, we accumulate the flow for one hour and then add this to the total.  You can use the PC software reset totals function which clears both the hour quantity and the total quantity.  At the end of your test you can add the hour quantity and the total quantity to give you the total flow during your test.

  • How to troubleshoot the PTX

    1. To check the voltage, using a multimeter measure between the Ground and Level Source. A voltage of between 10-12 V should be recorded.

    2. To check the current, remove the SENSE lead and connect it to a multimeter (set to current) in series. The current should measure between 4mA to 20mA depending on the depth of the PTX.

  • How do I connect the velocity sensor to the system unit?


  • How is the velocity measurement calculated?

    All velocity measurements are logged and stored as a histogram; the Mainstream has the ability to determine two velocities for the histogram.  The velocity check is the most frequent occurring figure.  The mean velocity  is the average of all the entries

    velocity check

    Mean Velocity  = S(velocity x frequency of occurrence)/no. entries

  • What does the Mainstream velocity histogram show?

    It shows the distribution of tracer velocities in the “zone of inspection” of the velocity probe


  • What is the specification for required “suspended particles”, ie minimum size, concentration and “ultrasonic consistency” to provide correct reflection. If it is different, specify limits for minimum and maximum velocity?

    All velocity probes give better than an 80% signal quality at a velocity of 80mm/S in our test rig which is filled  from a drinking water supply.  Therefore a minimal number of particles is needed to provide a signal.

  • Does this include “soft” biological particles as found in slow (< 0,3m/S) irrigation/drainage channels. Are they sufficiently reflective?

    This will not be a problem.

  • Where is the best place to mount the velocity probe?

    The sensor must be mounted in a position such that the sensor is always covered by at least 30 mm of liquid.  In larger open channels (e.g. trapezoidal) the sensor can be mounted either on the bottom or side of the channel.

  • How many sensors can be used with the Mainstream?

    The existing Mainstream product range can use only two level sensors and one velocity sensor.

  • How representative is the velocity measured at the location of the sensor with the average velocity across the channel section?

    The ultrasound from the probe can penetrate several metres into the flow and the velocity histogram from which the flow velocity is calculated is constructed from all verified velocity data in the received ultrasound.

  • How good is Mainstream at measuring low velocities?

    It is possible to configure the Mainstream to measure velocities as low as a few millimetres per second.  With this configuration the maximum velocity would be below 1 metre per second.  We consider that the main problem with very low velocities is that the air bubbles and particles on which the velocity measurement depends might separate from the flow.  We also suspect that in the situation of detecting flow reversals for use in a tidal control gate, the flow might separate into upper and lower layers traveling opposite directions.  In this case the velocity histogram would contain both positive and negative velocities and the Mainstream would give zero signal quality and zero velocity.

  • What is the turndown ratio of your product?

    Turndown ratio is 100:1 is often used to compare the span – the range – of flow measurement devices.

  • Why is upstream-facing standard and when is downstream-facing recommended?

    When the probe face is upstream, the flow is unaffected by the velocity probe.  When the probe face is downstream it must be shielded against large debris.

  • Is the probe scale factor dependent upon the flow direction?

    Probe scale factor is independent of the flow direction.

  • What is the minimum level, and maximum velocity respectively, without interfering with the measurement due to velocity/level-change caused by the displacement of the sensor?

    There are no restrictions provided the depth sensor is correctly sited.

  • What is the operating temperature of the probe?

    The maximum working temperature is 85º C; the air temperature is no more than 50º C