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PV = nRT
Where, P= Gas pressure
T=Gas temperature
V=Gas Volume
n=Number of gas molecules in moles
R=Ideal gas constant

Now if the gas is at specific temperature and pressure, the ideal gas law can be simplified to

V = n (RT/P) = nK, where K is a constant

Therefore, V ∞ n
Or, simply put, the volume of the gas becomes proportional to the number of molecules in moles at a specific temperature and pressure.

Volumetric flow rate is the rate at which a volume of a gas travels past a given location. Volumetric Flow = As Measured Volume of Gas / Time

Standardized (mass) flow rate is expressed as the rate at which the volume of a gas travels past a given location if the gas is at a specified temperature and pressure. From the ideal gas law if the temperature and pressure are held constant, the volume of the gas is proportional to the number of molecules.
Standardized Flow = Volume of Gas (at the standard temperature and pressure) / Time

Consider a cylinder of gas located in a 20 deg C ambient temperature set to exhaust at a flow rate of 2 cubic centimeters per min (ccm). Now, if this gas flow is warmed to 40 deg C and the gas flow rate is measured, it would indicate a much higher volumetric flow rate. As the temperature increases, the increase in the volume of the exhaust gas is directly proportional to the rise in temperature. Similarly, if the gas flow is cooled to 5 deg C and the gas flow rate is measured, it would indicate a lower volumetric flow rate. Even though the volumetric flow increases or decreases at different temperature conditions, the standardized flow compensated to 20 deg C would remain the same (2 cc per min). The relationship can be described using the ideal gas law below:

P1V1/T1 = K = Constant, Where V1 is standardized flow rate at 20 deg C
P2V2/T2 = K = Constant , Where V2 is the volumetric flow rate at 40 deg C
Therefore, P1V1/T1 = P2V2/T2

So, which type of reading reflects the flow rate most accurately? It depends on the application. For atmospheric pollution monitoring, volumetric flow is of concern since the measurement of interest is the volume of air at the ambient pressure and temperature conditions. During volumetric flow measurement, care should be taken to ensure the gas temperature and pressure being measured at the instrument does not change significantly from the sampling point.

Gas flow is defined as the volume of gas per unit time. Bios' DryCal™ technology measures gas flow directly by using a precisely known volume - the measurement cell -and the measurement from an internal clock that is triggered by optical detectors detecting the movement of the piston in the measurement cell.

Using this proprietary DryCal™ technology, our meters directly measure gas flow. Many other gas flow meters measure flow through indirect means of either a pressure drop across some sort of flow restriction or through the transfer of heat from the gas flow.

Because Bios flow meters measure gas flow directly with volume and time, they are largely immune to the affects of the gas species being measured. Gas humidity and gas temperature can degrade the accuracy of other instruments. Also, while some other instruments equipment ratings are given as percent of full scale, Bios equipment ratings are given as percent of reading.

STP Corrections used by DryCal Units

Vs = Vf  x  (Pg/760)  x  ((273.15+Tk)/ (273.15+Tc))

The Defender 510 measures volumetric gas flow.

The Defender 520 measures volumetric gas flow with displayed gas temperature and pressure measurements. This allows for manual calculation to standardized readings with a standard formula.

The Defender 530 measures volumetric and standardized gas flow readings.

The Definer 220 measures volumetric and standardized gas flow readings with a higher accuracy than the Defender with Swagelok® inlet and outlet fittings.

Connecting Volume is the gas volume between a flow generator and the instrument taking the measurement. Since gas is compressible, this gas can act as a spring between the flow source and the measurement instrument. For best accuracy this volume should be kept to a minimum.

We recommend keeping the tubing volume between the gas flow generator and the instrument below the values listed below.

Here is a list of several things to check. If you still have difficulty obtaining accuracy, feel free to contact Bios and talk to our application engineers.

• Verify that the flow source is connected to the pressure port of your meter for pressure sources and to the suction port for verifying suction pumps. The unused port should be at atmospheric pressure with any cap or plug removed. If you are calibrating a gas that requires an exhaust line to vent the measurement gas, ensure that the tubing is of sufficient diameter not to create a pressure drop greater then 5 inches of water.
• Ensure that hose and tube fittings are tight and leak free
• The tubing connecting your flow source (pump, mass flow controller, needle valve, sonic nozzle or restrictor) to the meter should be kept as short as possible. See the FAQ entry on "Dead Volume".
• Verify that you are measuring the correct type of flow and that the meter is set properly - volumetric or standardized (Note: Does not apply to Defender series, the DC-1 or the DC-lite, which only measure volumetric flow).
• If you are measuring standardized flow, check that the correct standardization temperature is set on your meter(Note: Does not apply to Defender series, the DC-1 or the DC-lite, which only measure volumetric flow).
• (Verify that the Sensor Factor on your meter is set to one, unless you specifically want it set to a different value (Note: this applies only to definer and ML models)
• Verify that the PTVM value for the meter is set to one (Note: this applies only to ML models).
• When calibrating MFCs or other flow generators, the gas pressure above the MFC or other flow generator should be 30 PSI or greater
• Temperature variations in the measurement environment should be minimized and the DryCal™ instrument should be thermally equalized to the environment for best accuracy.

Sensor factor is a number that can be entered into some models that multiplies the measured flow to scale the reading for certain types of calibrations. The Sensor Factor is a convenience feature that allows customers who are calibrating Mass Flow Controllers or other instruments with an alternate gas and need their readings scaled to compensate for calibration with an alternative gas. Care should be exercised to always verify that if the scaling factor is set correctly and we recommend always returning the scaling factor to one after completing a calibration.

PTV stands for Piston Tare Value; this is the amount of gas that passes around the piston during measurement. All Bios calibration equipment has a factory set Piston Tare Value that is stored in the memory of the DryCal™ cell. The value is typically very small 0.1 ccm for low flow cells, 0.2 ccm for medium flow cells and 1.4 ccm for the high flow cells. We adjust for this leakage by adding the Piston Tare Value (PTV) to the measurements.

On our highest accuracy instruments we allow for the adjustment of the Piston Tare Value with the Piston Tare Value Multiplier (PTVM). When using the instrument with gas species other then air or nitrogen, the molecular behaviors of these gases may degrade the Piston Tare Value. For highest accuracy, the instrument's Piston Tare Value (PTV) can be adjusted. Adjusting the Piston Tare Value is accomplished by entering a new Piston Tare Value Multiplier (PTVM). The Piston Tare Value Multiplier is multiplied to the Piston Tare Value and used to adjust the measurement; the default value for air and nitrogen is 1.000. The Piston Tare Value Multiplier (PTVM) can be set to any value from 3.000 to 0.2000.

For flows above 20 ccm, a new a Piston Tare Value Multiplier (PTVM) value can be calculated by using the viscosity of the gas being measured and accurate results will be obtained. Calculate the PTVM by taking the ratio of the viscosity of nitrogen to the viscosity of the gas under test. For example, to calibrate hydrogen consider the following: at 0° C, the viscosity of nitrogen is 165.31 microPoise, and the viscosity of hydrogen is 83.21 microPoise. Express these as 165.31/83.21, or 1.987, and enter 1.987 as the Piston Tare Value Multiplier (PTVM) for this cell.

When measuring alternate gases at flows below 20 ccm, or for absolute best accuracy, it may be necessary to perform a dynamic leak test using the gas under test. Contact Bios for information on this test.

Bios' viscous-sealed prover uses a piston and cylinder fitted so closely that the viscosity of the gas under test results in a leakage small enough to be insignificant. The leakage that does occur is tared out during the measurement interval (see Piston Tare Value for additional information). The piston and cylinder are of materials with match temperature coefficients of expansion and low friction so that Bios flow meters can operate under a wide temperature range without a change to their accuracy.

Gas compatibility should be considered when using a Bios primary standard to calibrate corrosive or hazardous gases. Our products are not intrinsically safe, and are not recommended for use with explosive gases. Also, materials within the wetted flow stream (the path of the gas being calibrated) may be damaged by corrosive gases. The Bios warranty does not cover parts or service labor related to use with corrosive gases.

Here is a list of materials within the wetted flow stream of each Bios primary standard:

DryCal DC-Lite
Aluminum
Black Chromate over Zinc
Borosilicate glass
Epoxy potting compound (3M Scotch-Weld Item #: DP-270)
Graphite
Mylar
Nylon
Nylon mesh inlet filter material
Silicone
Solenoid valve (magnets, windings, frame, cover, shaft)
Stainless steel
Teflon
Viton A

DryCal DC-2
Acrylic
Aluminum
Borosilicate glass
Brass
Epoxy potting compound (3M Scotch-Weld Item #: DP-270)
Graphite
Mylar
Nylon
Nylon mesh inlet filter material
Polycarbonate
Silicone
Solenoid valve (magnets, windings, frame, cover, shaft)
Stainless steel
Teflon
Viton A

Met Lab Series
Aluminum
Anodize
Black Chromate over Zinc
Borosilicate glass
Epoxy potting compound (3M Scotch-Weld Item #: DP-270)
Graphite
Mylar
Nickel-plated brass
Nylon
Nylon mesh inlet filter material
Pressure transducer
Solenoid valve (magnets, windings, frame, cover, shaft)
Stainless steel
Temperature sensor
Viton

Definer 220 and Defender Series
Borosilicate glass
Graphite
Viton
Mylar
Stainless steel
Zinc plated steel
Tin
Ceramic
Epoxy
Nickel
Polycarbonate

Definer 1020
Borosilicate glass
Graphite
Aluminum
Stainless steel
Epoxy
Viton
Nickel
PolyCarbonate

It is normal for your MetLab to display a temperature that differs from your laboratory's temperature. Our calibrators measure the temperature of the actual gas entering the flow cylinder. This is the temperature to which the volumetric reading must be standardized in order to give accurate readings. Room temperature or the gas' original temperature is not important, but the temperature of the actual gas in the cylinder is.

In normal operation in a very stable lab, the MetLab may indicate a temperature slightly higher than the lab temperature due to its internal heating. This is a normal effect, and can be minimized by not charging the battery during critical readings. The battery should be charged overnight prior to using the instrument so that extra heat from the charger is not introduced during the flow measurements. If already fully-charged, the battery can still be left connected to the power line. For the most critical flow readings (beyond specifications), the instrument can be operated on battery alone.

Our flow meters are made for gas flow use only, not for the measurement of liquids.

If you have drawn liquid into your flow meter, you should immediately send it to Bios for service, called "recertification." This service will include full product refurbishment, which will restore the instrument to as-new condition in most cases. In the rare event that liquid damage is permanent, additional repair costs may apply. The need for repair can only be determined during the course of product testing, which is a normal part of the recertification process.

ISO 17025 is the international quality standard for calibration laboratories, set forth by the International Organization for Standardization (ISO).

A network comprised of the national standards institutes of more than 145 countries, ISO developed its 17025 standard to assess the competency of testing and calibration laboratories. The requirements of ISO 17025 encompass all aspects of laboratory management, including calibration procedures, analytical testing proficiency, report generation and record keeping, and ensure calibrations are performed by properly-trained personnel using controlled test methods and procedures. ISO 17025 is to laboratory measurements as ISO 9000 is to products. Certification to ISO 9000 alone does not demonstrate a lab's ability to produce technically valid data and results, and all ISO 9000 elements relevant to the testing and calibration services within a laboratory's quality system are incorporated in ISO 17025.

Yes, Bios International is accredited to ISO 17025 by The National Voluntary Laboratory Accreditation Program (NVLAP). NVLAP, administered by The National Institute of Standards and Technology (NIST), provides third-party accreditation to public and private laboratories based on evaluation of their technical qualifications and ability to perform specific tests and calibrations compliant with ISO.

We are proud to state that our scope of accreditation appears to be the greatest of any ISO 17025-accredited flow facility in the world, at ±0.076% standardized accuracy. A copy is available upon request.

Our built-in self leak test is a quality control measure. It is not, however, a full product diagnostic, so your flow meter may pass the leak test, but still require service by Bios to restore the product to specification.

Essentially, the leak test shows whether the flow measuring cell has maintained its basic integrity. In other words, a leak test failure usually means that something is wrong with the instrument, causing unusual leakage of the gas being measured. On the other hand, a passed leak test is not "proof" of perfect performance.

Properly performing the leak test takes time, and should be done on a stable, vibration-free surface. If the leak test fails, you may want to try it again on a more secure surface.

The leak test is simply an easy way for you to check whether your instrument has a leak that requires immediate attention, Bios recommends that you perform the leak test only once or twice annually, in between sending the instrument to our ISO 17025 facility for service.

There are several possible reasons why your Bios primary standard's piston won't rise within the flow cell, or seems to "stick" within the flow cell (won't drop to the bottom of the flow cell after a flow measurement):

Possibility #1: Battery
Your Bios product's battery may be too weak to open the internal valve, which releases the piston from its top position within the flow cell once a flow measurement is completed.

If recharging the battery does not resolve the issue your battery may need to be replaced Please return your Bios product to Bios for battery replacement. Or, if it's time for your Bios primary standard to be recalibrated, we'll replace the battery free-of-charge as part of our Recertification service.

Possibility #2: Particulates or Corrosion
The interior of your Bios product's flow cell may become "dirty" and particulates, such as dust, can  affect the piston's free movement within the flow cell, Or, if your Bios primary standard has been subjected to a corrosive gas, any number of interior parts or mechanisms may be corroded.

Disconnect your Bios product from its gas flow source and then turn it upside down and then right side up a few times. , If the piston doesn't move freely and smoothly within the flow cell, then the piston and/or the flow cell interior may be affected by particles or corrosive gas. Return your Bios product to Bios for factory recertification.

Possibility #3: Sunlight
If your Bios product is used outdoors in direct sunlight, the flow cell's internal infra-red sensors may be affected, causing the piston to appear to "stick" within the flow cell, or not move at all.

Simply covering the flow cell with paper or your hand during flow measurements in direct sunlight will solve the problem.

Please note that the Definer 220 is often used to perform field verifications of environmental monitors, and therefore this product comes standard with "sunlight film" adhered to the interior of the flow cell.

However, other Bios primary standards, such as the Defender, Met Lab Series, or our discontinued DC-Lite, DC-2, and DC-1, were not intended for use outdoors, and do not have sunlight film protection. If you routinely use one of these products outdoors in direct sunlight, check with Bios as to the possibility of having sunlight film installed during your next annual Recertification.

Possibility #4: Valve
The valve may not be functioning properly. When this is the issue, often the normal "clunking" sound of the valve is no longer audible (this "clunking" of the valve is not to be confused with the quiet "clicking" sound of the electronic solenoid). This may be due to a weak or dead battery, or it may be a mechanical problem. Return your Bios primary standard to Bios for our Recertification service, or for basic repair if it's been less than a year since your last recertification (note the "Battery" section above).

Possibility #5: Application
Is a flow source attached to your Bios product? For a suction application, your Bios primary standard's Inlet fitting (Pressure fitting) should be open to ambient air, with its Outlet fitting attached to the flow source through tubing. For a pressure application, its Outlet (Suction fitting) should be open to ambient air, with its Inlet fitting attached to the flow source through tubing.

Bios primary standards, featuring our DryCal™ technology, are not intrinsically safe and are not for use with explosive or flammable gases, or for use in explosive environments. If you choose to calibrate explosive or flammable gases with your Bios instrument, please follow your organization's laboratory safety procedures, which typically require operation within an inert atmosphere. To enable use in an inert atmosphere, some of our models do provide gas Purge fittings.

Bios International is the only authorized service center for our products in the United States. TPF Control in Wijchen, Netherlands (www.tpf-control.nl/contact.html) can also service Bios International's DC-1& DC-2, DC-Lite, Definer 220, and the Bios Defender 510 and 520 products in Europe.

While we cannot not guarantee a specific return date, our normal service time is typically about 10 business days from the day we receive your Bios product to the day we return ship the product.

Expedited service (called 48-hour turnaround service) is available for DryCal Defender 510/520, Definer 220, DC-Lite, DC-1, and DC-2 products for an additional charge. Expedited turnaround is 2 working days from the date your DryCal arrives at our facility to the date it is return-shipped (excluding Saturdays, Sundays, holidays, summer flex time, or payment and paperwork discrepancies). For example, if we receive an instrument on Monday, it will return ship on Wednesday.

If we are unable to meet our 48-hour commitment for internal reasons, you will be notified as soon as possible and charged only the standard service fee. You will remain responsible for the standard service fee and associated return shipping charges.

Keep in mind that Bios does not begin service of your product until all appropriate paperwork, price approvals, and payment details are settled. The time it takes to settle these issues are independent of the service time. Your cooperation in providing Bios with all necessary paperwork and/or approvals will help ensure a faster turnaround time.

If the gas flow source connected to your equipment (such as a sampling pump) exceeds its rated flow range of the display will read "Over Range" and the piston may become "stuck" at the top of the flow cell. For example, DC-Lite model DCL-H is only rated to 30 liters per minute. If you attempt to use the DCL-H to calibrate beyond 30 liters, "Over Range" may appear in the display.

When the gas flow source is disconnected from the flow meter the piston should return to the down position and the "Over Range" display should clear. In most cases, the meter will be unharmed, although it is not recommended to use itabove its rated flow range, and Bios is not responsible for damage caused by exceeding the meter's rated flow range.

There are only 7 basic parameters used by national laboratories with international consensus as to their values. The 7 SI base units (International System of Units) are length; time, mass, temperature, electric current, amount of a substance (moles) and luminous intensity.

Other units, called SI derived units, are obtained from a system of equations involving the 7 SI base units. These SI derived units include volume and pressure (a combination of length, mass and time).

With no SI base unit for gas flow, it is necessarily a derived measurement. Volumetric flow consists of volume divided by time. To obtain volumetric flow, most national laboratories use provers similar to the Bios' primary piston provers, measuring the time it takes to displace a known volume of gas. These instruments are classified as primary because their readings are directly derived from the SI units.

Bios products featuring our DryCal™ technology (Defender series, Definer series, ML series and the DC-1 AND DC-2) are true primary standards in every sense of the word, because their accuracy is based upon primary SI units: The interior diameter of the glass measuring cylinder; the length of piston travel within the cylinder; and the time it takes the piston to travel this distance, implying a known volume. Our patented DryCal™ technology, therefore, offers accuracies at the level of national laboratories.

The only major difference between Bios products and the large, complex, delicate and expensive national primary standards is that our primary provers are small, shippable and easy-to-use.

Our normal hours of operation are Monday through Friday, from 8:30 AM to 5:00 PM EST.

From late May to early September, we are closed on Fridays. During this period, we will be open Monday through Thursday from 7:30 AM to 5:00 PM EST for your convenience.

Current and discontinued product manuals are on our website.