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Technical Questions

  • How does the alarm option on the VPFlowscope M work?

    The VPFlowScope M features an alarm option for condition monitoring. This alarm option can be configured with VPStudio. Upper, lower or a combination of these boundaries can be set as a condition level. To which of the 3 measurements the alarm is connected is up to the user. One of 3 can be chosen with the preferred unit, e.a.: m3n/hr, bar, SCFM, deg F, Kelvin, and many more.

    Download the full application note here: AN12-Alarm output

  • My VPFlowScope DP shows a value under the Qmin (minimum) value

    How is this possible? The DP has a specified Qmin of 20 mn/sec. Below this value, it is still possible to see flow values, because if internal averaging of the meter and due to the way it is calibrated. During calibration, we set the internal cutoff on 15 mn/sec, which enables you to see fluctuations around 20 mn/sec.




  • I lost the IP address of my Modbus/TCP converter. How can I recover this address?

    In the remote I/O modules we offer for VPInstruments, the IP address can be configured by 3rd party configuration software. Depending on the type of converter, you should go to the original equipment manufacturer, which provides a small software program. This program can sniff/search your computer network and will bring up a list of all devices. On most converters, there is also a re-set button which you can use to go back to factory default settings.

    VPInstruments uses converters made by ATOP, Anybus, Moxa and other brands. Refer to the original manual of the component for further details on how to re-set or re-configure these products. In the VPVision manual, you will find general instructions on Modbus/TCP based I/O modules. See download links for the individual manuals below:


  • Can you use a 35 bar flow meter in a 40 bar system?

    From a safety perspective: yes. We tested our products well above 40 bar. however, the pressure sensor in the VPFlowScope cannot measure higher than 500 psi (which is  a little more than 35 bar). Above this, the sensor will start to behave non-linear, and it will eventually clip. For further details, please check the safety guidelines for the VPFlowScope 40 bar version in the user manual.

  • Is modbus RTU always included in your flowmeters?
    Yes, of course! Modbus RTU is included. All our flow meters are equipped with Modbus RS485 and use the Modbus RTU protocol. The new VPFlowScope M even has Modbus/TCP. So why use old-school 4 … 20 mA when you can have all parameters at once via Modbus?Further reading on how to connect to a modbus network can be found here.
  • What is the difference between full “percentage of full scale” and “percentage of reading” accuracy?

    The accuracy of s sensor or to state it better: the measurement uncertainty can be specified in two ways.

    If a meter’s accuracy is based on a percentage of its full reading capability, the error is a fixed value. For example; an error of 0.5% of full scale, in a 150 m/sec device is +/- 0.75 m/sec

    At 10 m/sec, the error will be 0,75 / 10, which is 7,5%

    If the device has an error expressed as a percentage of the actual flow, then a 0.5% error of 10 m/sec is only 0,05 m/sec.


  • Can I use a lage T-piece as an insertion point?

    Insertion flow meters are great tools for compressed air measurements. But you have to be careful when installing these devices. The insertion hole has to be as small as possible, otherwise it will create a turbulence around the probe tip. This turbulence can cause misreadings. : in this case, you want to narrow the hole as close as possible to 0,5 inch, plus some tolerance for drilling. If this T-piece is still to be mounted, you can insert a small ring in between the two pipe ends to fill the space.


  • Where can I find the UL listing of VPInstruments products?

    A copy of the listing is found below:


    Mass flow meters, Series VPFlowMate, Cat. Nos. VPF-Rxxx-Mxxx-Dx-Sxxx-Exxx, may be followed by PN or PN 20, VPP-Rxxx-Pxxx-Dx-Sxxx-Exxx, may be followed by PN PN 20 or PN 40 where x can be any letter/number.

    Series VPFlowScope, Cat. Nos. VPS-Rxxx-Pxxx may be followed by PN, PN20 or PN40, where x can be any letter/number.

    The actual status can be checked here.  Search for Van Putten Instruments or E231429

  • What are the conversion factors for other gases?

    You can use the VPFlowMate and VPFlowScope with various gases, as long as they are non-corrosive and non-explosive.

    Examples are:

    • Helium
    • Argon
    • Carbon Dioxide
    • Corgon (C02-Argon)
    • Nitrogen
    • Breathing air mixtures

    For oxygen, special caution must be taken and additional regulations/ legislation may be applicable.  The grease in the VPFlowMate and VPFlowScope may not be approved for use with oxygen. Please consult your company on internal safety regulations and make sure that the wetted materials (anodized aluminium, stainless steel 316, glass and epoxy) are approved.

  • What is the service/ recalibration interval for my flow meter?

    We recommend to recalibrate your VPInstruments products annually. But the actual drift of the sensor mainly depends on the pollution rate or certain circumstances. For more information about the importance of recalibration can be found here or for an example:

    •  You would want to check your instruments before a major critical measuring project. Let’s say you are an auditor, then you would probably want to check your instruments before you take the plane to the next remote location.
    • After an event, especially if your instrument has been dropped on the floor.
    • Per requirements: if your company has an ISO 9001 certified quality management system, recalibration for critical measurement systems could be mandatory. Check your QMS on this topic.
    • Bi-annually. If you seldom do critical measurements and don’t expose your meter to an event, this can be more cost-effective.

  • What air quality does your flow meter need?

    The ISO 8573.1 air quality standard classes is the most suitable compressed air. It ensures that your factory will get the compressed air quality you specified. It can also be used to define the required air quality for sensors used in the compressed air network.


    The best air quality for solids is up to class 5. The after cooler and pre-filter of the compressor have taken out most harmful particles. An additional source of particles can be rust in the pipework. Using a general purpose 1 micron filter will take out any harmful parcicle


    The best air quality for water is up to class 6 (non condensing). We have not seen any significant effect on our flow meters. (for more information on water, read on below).


    For short audits, oil does not give any problems, however, a thin film may occur over time. We do recommend a regular check in permanent installations after six months. Once you determine that it is still clean, you can postpone a following check till after one year.

    Humidity Effects

    Thanks to its high operating temperature, the flow sensor will keep the surrounding air very dry. This minimizes the effect of normal humidity variations.

    Variations in Dew Point

    In our in-house test facility, we have researched the effects of dew point variations between -20 and +15° C (Class 3 … Class 6 according tot DIN 8573-1).  Our thermabrigde sensor does not show any significant change in sensitivity over this range, which covers most industrial compressed air applications where at least a refrigerant drier is installed.

    Condensation effects (droplets)

    Once condensation occurs, the gas temperature is close to the dew point temperature.
    Example: The air coming from an air compressor has a dew point of 35° C. The outlet temperature is around 50° C. As soon as the temperature drops below 35° C, the water vapor will condensate and form small droplets. Note that the thermal conductivity of water is about 25 times higher than air. Every time a water droplet hits the sensor, the amount of heat conducted to the medium will dramatically increase. Depending on the size of the droplet, the water will evaporate or it will temporarily cover the sensor. In most cases, large spikes can be seen in the output signal. In general, high readings up to 50% have been observed with thermal mass flow sensors.

    Solutions :

    1 Place the flow meter downstream of a refrigerant/ desiccant drier, or at least at a point where most of the water is separated from the air, for instance behind a receiver tank.
    2 When wet air is the permanent condition, a VPFlowScope DP is the best choice.  Please make sure that the installation conditions meet the specific requirements of the DP.

  • Which materials get in contact with compressed air?

    The wetted materials for all our thermal flow sensors are:

    • Stainless steel (316 and 304)
    • Anodized auminium
    • Glass
    • Epoxy
  • What is the measurement range of your compressed air flow meters?

    See our VPFlowScope leaflet for an easy to use range table.

    This table applies to the VPFlowScope and VPFlowScope DP compressed air flow meters. In this table, you can see the maximum and minimum flow values for specific pipe diameters. When you have a different diameter, use the VPCalculator on-line tool.

  • How can I read out the 4 ... 20 mA output

    The VPFlowScope and VPFlowScope M 4..20 mA outputs are active. This means they provide power to the loop. You can measure the output using a multi meter or PLC or building management system's IO modules. Check the user manual for details.


  • Are readings normalized to standard pressure and temperature?

    Yes! The VPFlowMate and VPFlowScope are mass flow based products. So they relate every measurement back to reference conditions.
    We chose for 0° C and 1013,25 mbar as these are global standards. You can convert this to FAD or to other reference conditions yourself.

    Additional pressure and temperature compensation is not needed! This saves you money and the data can be easily related to compressor specifications.

  • What is the connector pin out on the VPFlowScope?

    The pin out is the same for both the display module and the connector cap.

    See also the user manual.

  • What is the capacity of the VPFlowScope (DP, In-line, Probe) data logger?

    The VPFlowScope has a great feature: the data logging display! It contains 2 million points that can be assigned to three channels. You can change the measurement interval for the flow, pressure and temperature channel.

    Example: when you use flow, pressure and temperature all at 1 second interval, each channel generates 86,400 points per day. This will result in a full memory in about eight days with the 2 M points memory).  See the user manual for further details. The old type displays have 500,000 points.

    To save memory capacity for flow, pressure and temperature, the real totalizer values are not stored in the data logger memory. We only store the initial totalizer value. VPStudio calculates the totalizer values using actual flow and the time interval. This can lead to differences between the actual totalizer as seen on the display and the calculated totalizer from data log sessions. In any case, you can always check the display directly after the air audit, to get the actual totalizer value.

  • How do I connect the VPFlowScope to a Modbus RS485 network?

    All VPFlowScope mass flow meters are equipped with a Modbus RTU interface. The VPFlowScope M includes the Modbus RTU protocol as well as Modbus TCP protocol and connectivitie. This makes connecting to a modbus RS485 network very easy, provided that you are an experienced modbus user. If not, please visit modbus.org to read more about the basic principles. Or read this application note.


  • How can i access VPVision

    VPVision can be accessed in multipe ways: There are several options to access the VPVision system • Connecting the VPVision system to customers Ethernet will enables everyone connected to the same network to access the system by using the fixed IP-address with any laptop, tablet or smartphone. • Setting up a VPN (Virtual Private Network) connection. This will enable users to access the VPVision system from anywhere in the world with a username & password. This is also a very fast and easy way to provide support the customers from the factory. • Connecting a 3/4G module to the VPVision will allow you to access the system from anywhere in the world. The difference between this method & VPN connection is that this does not require the VPVision system to be connected to the customers Ethernet. • Connecting a WiFi module to the VPVision computer allows you to access the VPVision software wirelessly within close range of the main cabinet. Please note this would also be possible when connected to the Ethernet of the customer and you are connected to the same network with WiFi.

  • How can i integrate VPVision with the exisiting BMS/PLC/SCADA?

    VPVision can be integrated with your exisiting system with the SQL module. All data will be stored in two data bases.

  • How can i expand the VPVision energy management system?

    VPVision is easy to expand. We can add sensors to your existing or new hardware and the software can also be easily expanded with optional items and additional sensors. We can update the software remotely. You can also use existing sensors with 4 … 20 mA signals. VPVision grows and adpats according to the needs of your company.

  • When you want to achieve the internal goals / KPI set by management

    A monitoring system should allow you to:

    ·        Set upper and lower thresholds for amounts of consumptions and potentially alarm you.

    ·        Shows you if you are performing better or worse reflected to a certain period.

    ·        When you’re in need of clear performance indicators, like specific power, total consumption and money per time frame spent on running production equipment.

    ·        When visualization and changes of your performance indicators should be easy to display to internal clients, i.e. Higher and middle management and different operational members and floor workers to show the actual performance, acknowledge their sustainability efforts and further create awareness.

  • When you need something to visualize what’s going on

    ·        Monitoring helps you understand how your system acts which the change in demand. See energy consumption goes up when producing a different batch, see the standby and offload hours of your compressors, get an idea of your energy baseload, your base air leakage load, the big energy and gas consumers or even identify why different operators use more or less air than others. See the change of you dew the point with the change of seasons or the increase of plant air demand, take appropriate actions before system failures occur and lead to an expensive system shutdowns, expensive maintaining services, and non-operating and production hours or even the loss of produced goods.

  • When you want to identify big consumers

    ·        When committed to ISO regulations, like ISO 50001. It prescribes that large energy users need to be identified. Identification can be done by making use of energy meters, gas or liquid meters or other consumption meters together with a data collection system.

    ·        When machine or machine park consumption needs to be measured, an optimization plan needs to be created, agreed measures to be put into effect and the outcome measured and monitored. All according to the plan, do, check and act methodology. Monitoring helps you to plan, do and check. The “act” in this process can be taking away leakages, adjust motor controls, lower machine pressure or complete machine or process redesign. It can be a manual operation of a minor change or taking away a cause that will lead to a better performing machine or overall process.

  • When you need to optimize and quantify energy saving activities

    How do you know what savings you have obtained by making a certain change? How much better do you perform?  How much less electricity, gas or liquid is the machines using? Do you only measure in product output? What about the input? Monitoring provides you key data before and after your saving and optimization activities. It helps you set quantify consumption per item produced, allowing you to truly cost allocate.

  • When you currently have lack of monitoring and management tools

    When you are not a user of a monitoring platform yet, it means you’re running blind. Years of experience may help you get an idea of what needs to be done annually to maintain your production output. But not trending energy, gas or liquid consumption, leakage and production output, may mean you are burning money and time from the day you have started and have seen unnecessary production standstill. Breakdowns, overconsumption or even underperforming machines, could have been easily spotted well in advance. When trending system parameters, setting upper and lower thresholds and receiving alarm notifications, you can be ahead of machinery breaking down, start to consume tremendous amounts of energy or maybe pollute your end product.

  • When you also need easy reporting to the internal organization
    • When your company charges departments an equal share to cover the monthly energy bill while you know your department is not the biggest consumer? Are you being billed for energy, gas or liquid usages based on assumptions?
    • When monitoring different areas or per different production zones, monitoring will help you identify who is consuming when, where and what. A weekly or monthly report that combines energy usage with gas or liquids usage can neatly summarize the true share of a department of the total energy bill together with all other utilities.
    • Reports can then be send internally to the financial officer, head of productions, the CEO or whoever needs the actual data. It will show which department needs help for further energy optimizations programs. Target your biggest consumers!
  • Where do you need a monitoring system?

    1.     Where there is more than 75 kW or 100 HP compressors are installed

    ·        The general rule of thumb we use is any company that uses a 75 kW or 100 HP compressors for more than 12 hours a day have an opportunity to save money. The bigger the combined installed kW or HP, the greater the savings potential.

    ·        Where costs for air are being billed, either to an internal client or to a neighboring facility.

    ·        Where you face big interconnected compressor installations with ring systems and feed ins from all over the plant. Those deserve to be well monitored to check where air is coming from and if compressors are not “fighting” each other.

    2.     Where energy pricing is rising rapidly

    ·        If energy becomes an expensive resource, compressed air installations hold a very potential for cost savings. Remember that only approximately 7.5 % of the energy into the compressor is used usefully to support production machinery.


    3.     Where the air is not the 4th, but the 2nd most important utility after Electricity

    ·        When air is vital to your processes and day to day activities to maintain your desired output, you better make sure you service your equipment in time or your service provider comes in when he is needed. How to save money on service costs? To measure and monitor if his service is really required. How to know if what he did is having the desired effect? Monitor the results of your or his work.

  • What sensors can be connected to VPVision?

    VPVision supports all VPInstruments sensors, and other Modbus RTU or 4 .. 20 mA based sensor types. For some second party Modbus sensors, we offer pre-installed drivers for quick and easy installation. With others, like Hart or Profibus based sensors, we make use of converters. 

  • How can i configure VPVision

    VPVision can be configures by accessing the system and following it step by step. More details about this in our manual.

  • How can i extract data?

    With the CSV widget you can extract data in CSV format.

  • What type of visualizations are possible?

    There are a lof of different types of visualizations possible:
    • Dashboard
    • Pie chart
    • Line graph
    • KPI
    • Area chart
    • Bar graph
    • Variation chart
    • P&ID with real time measurements