We've collected the most frequently asked questions about our Gen-Sys products on this page. If your question isn't answered here, please don't hesitate to contact us.Back to product page
What is the OVG-4 Calibration Gas Generator?
The OVG-4 is an instrument that can generate accurate, precise, and repeatable calibration gases for applications ranging from sensor/instrument tests and calibration to generation of test atmospheres in corrosion chambers.
What is a permeation tube?
A permeation tube is a small PTFE tube filled with the calibration analyte. When precisely heated the analyte diffuses through the tube at a controlled rate to generate an accurate calibration gas. Have a look at our permeation tube FAQ for more info.
Does the OVG-4 generate traceable calibration gases?
Yes. The permeation tubes are gravimetrically calibrated to NIST/UKAS traceable primary standards. Each tube comes with its own calibration certificate.
What and how many calibration gases can the OVG-4 generate?
Generating new calibration gas standards is as easy as inserting a permeation tube into the OVG-4. You can request pricing and availability and also watch a video of the OVG-4 in operation and see how easy it is to generate new calibration gas standards.
Can the OVG-4 provide mixtures of multiple calibration gases simultaneously?
You can put multiple tubes into one oven to generate a gas mixture. If you want to control individual concentrations, you can attach the outputs of multiple OVG units together to generate arbitrary calibration gas mixtures.
How do I calculate the calibration gas concentration generated by the OVG-4?
Each permeation tube comes with a calibration certificate. These values are entered into the Owlstone OVG-4 concentration calculator software along with the instrument settings to obtain the concentration of gas.
What is the lowest and highest calibration gas concentrations I can generate with the OVG-4?
This depends on the permeation rate of the tube, the flow, and the temperature. The OVG-4 can typically generate calibration gas concentrations from tens of parts-per-trillion (ppt) levels up to tens of parts per million (ppm).
What sample flow rates are attainable with the OVG-4?
The sample flow from the OVG-4 is controlled by a mass flow controller and can be adjusted from 50 mL/min up to 3 L/min. This can be further diluted with an arbitrary make-up flow to generate any total flow required for your application.
Can I further dilute the output of OVG-4 with a make-up flow?
Yes, the output of the OVG can be blended with a make-up flow. The Owlstone OFC Flow Controller allows you to blend additional flows and the OHG Humidity Generator allows you to blend with humidified air for complete environmental testing.
Can I change the calibration concentration but keep the total flow the same?
Yes. Owlstone has developed a unique split flow capability that allows you to change the concentration while keeping the total flow the same. This is very useful if you are testing/calibrating flow sensitive sensors or instruments.
How accurate and repeatable is the calibration gas generated by the OVG-4?
You can achieve target calibration gas concentrations with a +/-5% error. The unit is incredibly stable and repeatable over time. The sample flow is controlled with a mass flow controller and a large thermal mass incubation oven is adjustable to the temperature at an accuracy of +/- 0.1°C.
Can I control the OVG-4 through software?
Yes, the temperature and flow can be controlled through the software provided with the OVG-4. In addition, there is an RS-485 port that allows you to integrate the OVG-4 into your custom test setup (e.g., LabVIEW) for fully automated control and integration.
Is the OVG-4 system modular? Can I add more units later?
The system is fully modular. The OVG-4, OHG Humidity Generator, and OFC Flow Controller can easily be added or removed from the 19" Gen-Sys rack. You can get a single OVG-4 and the other two empty slots are blocked off. If you want to extend your calibration gas capability in the future, additional units can easily be added to the empty slots.
What else do I need before I can use the OVG-4 Calibration Gas Generator?
You can download the the pre-installation guide to see what else you need to get started.
Do I need to heat the transfer line from the OVG-4 to the sensor/instrument under test?
For low volatility compounds we would recommend using a simple wrap heater on the transfer line to avoid analyte condensation and memory effects.
How much training is required to use the OVG-4 Calibration Gas Generator?
In short the OVG-4 is very straightforward to set up and use. You can download a copy of the user guide to see for yourself.
What warranty is offered for the unit?
One year limited warranty. We also offer extended warranty options.
What servicing is required and when?
We recommend that the mass flow controllers are recalibrated once a year.
Is the OVG-4 CE certified?
Yes, the instrument is fully CE marked and certified to ISTA 3A.
Where can I view the full OVG-4 technical specification?
You can download a pdf version. You might also want to take a look at the user guide.
How does the permeation rate vary with temperature?
If the permeation rate (mg/cm) at one temperature is known, the permeation rate at a new temperature can be calculated using this equation, Log PRnew(ng min) = LogPRold (ng min) - 2950 (1/T1(k) -1/T2(K)), which equates to a change of 10oC you effectively double the permeation rate. Our experience has shown that using this rule is generally accurate to =/-5%; however, it should be used as an approximation only because some analytes will exhibit a larger degree error.
What’s the difference between OVG-4 and V-OVG?
The V-OVG has a larger bore oven, compatibility with diffusion tubes, and digital control of split flow and sample flow.
Both instruments can have multiple tubes. The OVG-4 Calibration Gas Generator can have 2 to 3 tubes and the V-OVG’s larger oven can accept 6 tubes.
How much do permeation tubes cost?
Permeation tube costs depend on the analyte, but are generally in the range of $199–$399. And of course, you can make your own tubes with the kit.
What consumables do the calibration gas generators use?
There are no consumables apart from the tubes you make. So–no variable cost.
What is the difference between a permeation tube and a diffusion tube?
There’s a size difference, and diffusion tubes allow you to generate much higher concentrations. There is a bit more concentration flexibility with the diffusion tube because it can vary from a PDMS membrane to a variable bore capillary. Diffusion tubes are also refillable. We normally put in a few grams of material.
What about "sticky" gases like formaldehyde? Could they persist in the instrument and prevent its later use for other compounds, such as nitrogen dioxide, or hydrogen sulfide?
We initially designed the OVG-4 Calibration Gas Generator so we could test "sticky" compounds such as explosives and taggants. As such, we designed it so the internal flow paths are all passivated with Siltek treatment and are heated. We do not see blockage issues even for compounds with very high boiling points e.g., explosives.
Is there a specific set of Mass Flow Controllers (MFC) we should be looking at with the OVG-4 that would allow us a maximum range of dilution?
The OVG-4 Calibration Gas Generator has an internal MFC. We can customize as required up to several liters per minute–standard spec is 50–500 ml/min.
I would like a setup where both pollutant concentration and humidity could be controlled. Are OVG and OHG designed to be connected?
Yes, the systems are completely modular and are designed to run alongside each other to generate a humidified gas stream.
How long does the water last in the OHG?
Generally, 500ml of water will last at least a couple of days at 3000 ml/min. At higher flow rates, the water will need refilling sooner, and vice versa at lower flow rates (the rate of depletion is proportional to the flow rate).
What is the permeation rate for my analyte?
The permeation rate is measured after the tube has been built and calibrated by measuring mass loss over time. A calibration certificate will be provided.
What does a calibration certificate show?
Here is an example calibration certificate for formaldehyde.
Do you supply the V-OVG/OVG-4/OHG module without chassis?
Not at the moment. The chassis is needed to route power, flows, etc.
The standard chassis has room for 3 OVG modules. Do you have a chassis for one module?
Unfortunately, this is not offered at the moment. Only the 3-module chassis is offered.
Do you have a distributor in my country?
Contact us for a list.
My sensor has a sensitivity to flow. How do I ensure a constant concentration of my analyte at an arbitrary flow rate?
Our split flow capability is very useful when you test sensors that have a degree of flow sensitivity.
Can I control the kit from a PC?
You can download all the drivers from our support website.
Many of our academic partners use LabVIEW to build integrated rigs with generation capability.
How long do permeation tubes last?
Up to a year under continuous use.
Are permeation tubes reusable or single use?
Reusable. They can be used continuously, or taken out of the device and put back in again when required.
What other resources are available online?
You can browse documentation and resources on our support site. Some particularly relevant documents include: