What is the impact of a different reference temperature?
The reference pressure in all units is designed for 1013.25 mbar. If you want to calculate the difference between 0 °C and 20 °C, e.g., the formula is as follows:
(flow at 0°C /273.15)*293.15
(Law of Boyle/Gay-Lussac)
Example: 100 ln/273.15*293.15 = 107,32 ls (=7.3%) This corresponds to a correction of 0.366 % per degree Celsius
How significant is the impact if the operating conditions change (pressure and temperature)?
The thermal mass flow meters and controllers directly measure the number of gas molecules (=mass), which flows past the sensor. The thermal flow measurement principle is therefore insensitive to changes in pressure and temperature. Vögtlin calibrates each unit on two temperatures and a temperature sensor in the gas stream compensates any minor temperature error due to temperature effects in the electronics. Due to this compensation there are almost no measurable temperature effects in the range of between 0…50 °C.
What reference conditions (pressure and temperature) are the devices specified for?
Unlike liquids, gases can be compressed. The volume changes when the temperature and/or the pressure change. When specifying a gas volume, the reference temperature and the reference pressure must thus also always be specified. The flow unit is than referred to as normalized (f.i. ln/min) or standardized flow (f.i. ls/min)
When we refer to “Normal” flow we in general use:
Temperature Tn = 273,15 K, corresponds to 0 °C
Pressure Pn = 1013,25 mbar abs
When we refer to “Standard” flow we in general use:
Temperature Tn = 293,15 K, corresponds to 20 °C
Pressure Pn = 1013,25 mbar abs
See also: http://en.wikipedia.org/wiki/standard conditions
Please note: Not everyone understands standard conditions in the same way. In the case of reference pressure, everyone agrees, but in the case of reference temperature, there are differences:
To avoid misunderstandings, the reference conditions are specified clearly in our correspondence.
On request, we also deliver the devices with another reference temperature.
How can the devices be controlled?
The measuring and regulating parameters of the red-y smart series and red-y industrial series can be read out or controlled in an analog, manual and digital manner.
What is required to let the devices communicate to a PC?
Vögtlin offers a wide range of accessories, so that the devices can be operated directly via a PC with very little effort. In detail:
» Cable accessories for the red-y smart series
The free software get red-y offers a wide range of possibilities in context with the digital communication:
In addition, the following functions can optionally be unlocked:
Measuring range too large/small: Can the full scale of the device be adapted on site?
The mass flow meters and controllers of the red-y smart series and red-y industrial series have a very large dynamic range and can be converted to a certain extent on site.
A measuring device can be reprogrammed with the help of our service department by means of the get-red-y software. You will receive a password (valid for one day) for enabling this advanced function. Please contact our service department for more information.
Can the devices also be used in low pressure?
On principle, it is possible to utilize our thermal mass flow meters and controllers in the low pressure range. The sensor allows for an accurate flow measurement down to 100 mbar abs (we never verified lower pressures).
In the case of the flow regulators, a the low pressure is most of the time downstream of the control valve. The valves are vacuum-tight. The following must nonetheless be taken into consideration:
What information are required for selecting & sizing the mass flow meters & controllers?
Always provide a description of your application, why and how you want to use the units in your process.
At the very minimum we need the following information:
Does the mounting position need to be considered?
Basically, the red-y for gasflow mass flow meters and mass flow controllers can be installed in any position. At higher pressures and with dense gases such as krypton, a slight zero-point drift may occur. We therefore recommend using the devices horizontally wherever possible.
For the red-y smart pressure controllers with a small measuring range, the mounting position must be known. The dead weight of the pressure measuring cell can cause a zero point drift.
Does a massflow unit need a warm up time?
No, all red-y for gasflow devices are ready for immediate operation.
What is the impact of the moisture of the gas?
Moist gas of up to approx. 80 % rh has only a slight impact on the measuring accuracy. However, make sure that no condensation can take place in the measuring device. The condensation could settle on the sensor which could lead to inaccurate measurements. In the event that a measuring device has come into contact with condensation, it can for the most part be rinsed with a dry gas, such as N2. See also the remarks in the operating instructions.
What device parameters can be changed on site?
The device parameters will be configured in the factory prior to delivery according to the data provided by you.
The following parameters can be set changed with the help of the get-red-y software:
Do I have to place a filter in the gas line to the flow meter/controller?
If you use gas from a bottle which is clean and dry, there is, in general no need for a filter.
However, there is a risk during start-up of the devices, because dirt particles could be present in the line. It is recommended to install a bypass system, so that the line can be rinsed or can be exposed in response to possible repairs.
In the event that ambient or compressed air is used, the installation of a moisture and dust filter is strongly recommended.
Troubleshooting: Is there a checklist?
Within the troubleshooting pages in the operating instructions, we have summarised error patterns, possible causes and possible measures. If you do not recognise your error pattern or the suggested action is unsuccessful, please contact your Sales Ppartner. If you return the appliance, please refer to the ‘Returns’ section in the operating instructions.
How can the devices be cleaned?
Depending on the type of contamination, the devices can be cleaned on site. You can find more information on this topic in the operating instructions.
Is there a possibility for a remote maintenance in the event of malfunction?
Yes. In some cases it is convenient when we can access the client’s PC directly and solve issues online. Please contact us!
You can download the free software TeamViewer for remote support here.
What are the delivery terms to Germany?
We can handle deliveries from Switzerland to Germany quickly and easily:
Delivery time
Our units are manufactured according to customers specifications. Depending on the product and the workload, it takes one to three weeks from order to delivery. Please contact the factory for the current delivery time. We deliver the products to Germany twice a week.
In urgent cases, individual express deliveries are possible. In that case, the carrier will invoice the German VAT (Value Added Tax) directly to the addressee.
Customs and value added tax
We deliver your goods duty paid and tax paid from Germany. We do not charge any administrative fee.
Shipping costs
We charge you shipping costs, which, thanks to bulk shipments, approximately the rates of the German Postal Service. Vögtlin Instruments GmbH pre-pays the costs for customs clearance.
Invoice
You will receive an invoice in EUROS, including value added Tax. You pay the invoice amount to our account EURO-account at a Swiss bank (UBS).
Periodic calibration: How often do the devices need to be calibrated?
In principle, the user himself determines the calibrating interval. People often use one per year or in case of very clean gas, one per 2 years. The following questions/points can be helpful:
We suggest the following calibration interval:
1. First inspection after one year
2. After several calibrations have been made in succession, the deviation of calibration to calibration must be evaluated. Based on these data, a decision can be made to adapt the calibrating intervals.
The following influences can lead to an increased deviation:
1. No stable flow, caused by pulsating pumps, e.g.
2. The gas condenses or carries along liquid or dusty particles (applications with ambient air are particularly susceptible to contaminations. A filter needs to be provided here).
3. The effective pressure deviates considerably from the calibrated pressure (+/- 0,2%/bar).
4. The gas/gas mixture is not consistent with the calibrated gas.
5. The aging of electronic components can cause changes, sometimes even improvements. Electrical changes appear as a result of aging or gradual burning of components, which impact the quality of the output signal.
How does a variable area flow meter work?
A VA-flowmeter consists of a tapered tube, typically made of glass with a ‘float’, actually a shaped weight, inside that is pushed up by the drag force of the flow and pulled down by gravity. Drag force for a given fluid and float cross section is a function of flow speed squared only.
A higher volumetric flow rate through a given area increases flow speed and drag force, so the float will be pushed upwards. However, as the inside of the VA-flowmeter is cone shaped (widens), the area around the float through which the medium flows increases, the flow speed and drag force decrease until there is mechanical equilibrium with the float’s weight.
Floats are made in many different shapes, with spheres and ellipsoids being the most common.
The variable area flow meter for gases is highly dependent on the pressure in the measuring tube. The position of the control valve must be considered thereby (see also valve at the inlet or outlet).
What conditions (pressure and temperature) are the devices designed for?
Gases can be compressed. Consequently, pressure and temperature (and the kind of gas) have a direct impact on the display of the flow meter. We therefore calibrate the unit for the specific customer conditions that have been provided at the time of the order.
The flow values indicated on the flow table or on the measuring tube always refer to the depressurised state at 0°C and 1013.25 mbar abs. A different reference temperature or reference pressure is not possible.
If the temperature and pressure varies a lot we recommend you us a digital red-y compact flowmeter unit which automatically compensates for changes in pressure and temperature.
Valve at the inlet or outlet: What are the bases for the decision?
The following principles apply:
It is significant for the design that conditions, which are as constant as possible, are to be strived for in the measuring tube. The application determines the point of installation of the regulating valve. Most of the processes are close to atmospheric at the outlet side. In this case, the flow control valve is placed on the inlet.
There are processes, in which the pressure is not stable downstream from the flow meter. In this case, the regulating valve needs to be placed at the outlet. Warning: In this configuration, it is very important for the adjusted inlet pressure to be stable and to coincide with the designed pressure in the measuring tube. This arrangement is considerably more stable, because the depressurizing takes place downstream from the regulating valve (see also stable flow in response to changing conditions).
Create a stable flow at fluctuating back pressures
A flow can be stabilized with a simple trick in the event of an unstable back pressure. When using regulating valves, the following principle applies in the case of stable system pressure: The flow remains constant, provided that the downstream pressure does not exceed 50% of the inlet pressure.
This principle can be applied to all regulating valves from our assortment of goods.
What process information is required for the design of the measuring device?
We require the following information in order to provide you with an optimal solution: gas type, desired measuring range, temperature, inlet pressure and outlet pressure. It is wise to submit the range under which these variable change as well.
Where can the measuring value be read on the variable area flow meter?
The center of the sphere, thus where the sphere has the largest horizontal diameter, serves as read-out point.
Which measuring scales are available?
By default, a direct reading standard scale for air is setup according to the data sheet.
If you use the meter for a different gas and/or for different operating conditions, you can use the conversion factors which are listed in the data sheet.
The direct reading scale (also called product scale) is designed for a fixed operating condition.
The millimeter scale is used when the customer wants to use the meter under different operating conditions. For this purpose, appropriate tables are provided.
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Vögtlin Instruments GmbH
gas flow technology
St. Jakob-Strasse 84
4132 Muttenz, Switzerland
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