Velocity. Monitoring Instruments. Velocity measurement technology. Mini wind tunnel. Anemometer with telescopic probe. Anemometer with probes

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2 Monitoring Instruments 119 Velocity Velocity measurement technology Mini wind tunnel Anemometer with telescopic probe Anemometer with probes testo 425 testo

3 120 VELOCITY Velocity measurement in VAC systems Ambient conditioning in the pharmaceutical industry Air exchange and air flow are directly related to temperature and moisture in air conditioning and ventilation. Air flow is therefore an important parameter for modern ambient conditioning. The generation of physiological comfort levels in living and working areas is also becoming increasingly important for production areas. Specific climatic conditions are now more frequently required for processing, finishing or storing sensitive products. Testo`s measuring instruments have proved themselves worldwide in the qualification and validation of the high quality standards of such production units and products. Ambient conditioning starts with the fresh air requirements of humans. Adequate amounts of unused air are required, depending on physical activity. In addition to parameters such as temperature, humidity and CO 2 levels, flow velocities are also essential components when assessing comfort conditions. Targeted air streams carry out additional jobs in production facilities. Examples can be found in extraction systems where contaminated air is conveyed in a certain direction; or in clean room technology to create specific positive pressures. The necessity to generate a comfort and process climate using resource and environmentfriendly air is the result. Ambient conditions become process conditions One company which deals with ambient conditioning in relation to the planning, execution, qualification and validation of supply and production units for pharmaceutical, biotechnological and chemical industries is the LSMW GmbH from the JENOPTIK Group. The sensibility particularly of pharmaceutical products requires specialized expertise. Climatic conditions such as temperature, humidity and air exchange become process conditions. A defined air exchange number has to be verified when manufacturing certain products. Ambient conditions vary according to cleanliness class in which different pressure stages are to be retained via air currents in 10 or even 5 Pascal stages. Data management and calculations with testo 400 Testo measuring instruments facilitate, in particular, the operation and qualification of and demand-oriented checks on air conditioning/ventilation units. In addition to other instruments, the testo 400 multi-function measuring instrument, with several value measurement methods, is also used. One main task is flow measurement in ducts using 16 mm vane probes. Thomas Nagai from LSMW has the following to say on this topic: The newest VAC module update helps us to determine volume flow with its automatic calculation of the measurement points in the duct which are necessary in compliance with VDI 2080 or EN The coordinates required for a grid measurement are shown in the instrument display and can be completed quickly. The instrument calculates the mean values for velocity and volume flow, at the touch of a button, while taking into account the overall uncertainty of the measurement. Data specific to location is saved and then transmitted to your PC. This reduces your workload when measuring on location, saves on manual time-consuming calculations and facilitates standardized documentation." Temperature, humidity and pressure measurements are of major importance when analysing readings. Once the resulting correction factors are entered, they are then automatically taken into account by the instrument. It is not necessary to adjust the readings with correction tables. In this context, the absolute presure probe in testo 400 has many benefits.

4 121 VELOCITY The automated measurement procedure is supplemented by a practical reading handling function. On-site documenation with graphics and protocol printout is also possible. The ComSoft 3 software also offers the option of long-term checks with a predefined number of readings taken over time. Thomas Nagai is Group Manager at the LSMW GmbH and is responsible for the initial operation of technical building systems. His group originally came from the pharmaceutical division of M+W Zander GmbH in Nuremberg, a company which was also once part of the JENOPTIK Group and was integrated in an effort to concentrate all pharmaceutical activities in the LSMW GmbH. With respect to the cooperation with TESTO, Thomas Nagai emphasizes: The efficiency of the reference measuring instruments as well as their unique functions have been the basis of a very close partnership which has developed over the years. A constant exchange about experience in the field is important in the further development of products. One additional advantage is that the measuring instruments are calibrated on a regular basis in the accredited laboratories of Testo CAL GmbH. testo 400 multi-function measuring instrument Thomas Nagai, Group Manager, LSMW GmbH

5 122 Measuring and application ranges of the velocity probes m /s 100 Thermal probe up to +70 C Vane probes up to +60 C Vane/temperature probes to +140 C to +350 C Pitot tube to +600 C NiCr-Ni Pitot tube -40 to +600 C Probe selection The flow measuring range 0 to 100 m/s can be divided into three sections: Low-speed velocity 0 to 5 m/s Mid-speed velocity 5 to 40 m/s High-speed velocity 40 to 100 m/s. Thermal probes are used for accurate measurements in the range 0 to 5 m/s. Vane probes are ideal for velocities from 5 to 40 m/s. The measuring range of the Pitot tube depends on the differential probe used. The new 100 Pa probe can therefore be used for the exact measurement of the flow speed from approx. 1 m/s to 12 m/s. The Pitot tube yields optimum results in the higher velocity range. An additional criterion when selecting the correct velocity probe is the temperature. Thermal sensors can normally be used at up to approx. +70 C. Special design vane probes can be used to maximum +350 C. Pitot tubes are used for temperatures above +350 C. Thermal probes The principle of the thermal probe is based on a heated element from which heat is extracted by the colder impact flow. The temperature is kept constant via a regulating switch. The controlling current is directly proportional to the velocity. When thermal velocity probes are used in turbulent flows, the measured result is influenced by the flows impacting Thermal hot wire probe for measuring velocity, with direction recognition function the heated body from all directions. In turbulent flows, a thermal velocity sensor indicates higher measured values than a vane probe. This can be observed especially during measurements in ducts. Depending on the design of the duct, turbulent flows can occur even at low velocities.

6 123 Location selection You should measure in a straight part of the duct, if possible. The duct part should have a minimum of ten diameters of straight run before the measuring spot and four diameters of straight run after the measuring spot. The flow profile should not be interrupted in any way by flaps, dips, angles etc. Direction of flow 10 x D 4 x D D Vane probes The measuring principle of the vane probe is based on the conversion of a rotation into electric signals. The agent which flows makes the vane rotate. An inductive proximity switch counts the revolutions of the vane and supplies a pulse sequence which is converted in the measuring instrument and is then indicated as a velocity value. Large diameters (Ø 60 mm, Ø 100 mm) are suitable for the measurement of turbulent flows (e.g. at outlet ducts) at smaller or medium velocities. Small diameters are more suitable for measurements in ducts in which case the duct cross-section must be 100 times bigger than the probe crosssection being impacted. The 16 mm probe has proven to be very versatile. It is large enough to have good starting qualities and is small enough to withstand velocities of up to 60 m/s. Positioning in the air current The vane probe is set exactly if the flow direction is parallel to the vane axis. If the measuring probe is turned slightly in the air current, the value shown in the instrument changes. The measuring probe is positioned exactly in the air current if the value shown is at max. When measuring in a duct there should also be a minimum of ten diameters of straight run before the measuring spot and four diameters of straight run after the spot for best results. By design, vanes are less influenced by turbulence than thermal probes or Pitot tubes. Measuring velocity in ducts As part of approval measurements, indirect measuring procedures (grid measurements) are used to measure air flows. The following procedures are suggested in VDI 2080/EN 12599: Send for more details! You will find lots of information on air velocity measurements in the informative Testo HVAC technical manual Trivial procedure for grid measurements in square cross-sections Centroidal axis procedures for grid measurements in circular cross-sections Loglinear procedure for grid measurements in circular cross sections. M E A S U R E M E N T T E C H N O L O G Y

7 124 Supply/Returns The air vent greatly changes the relatively uniform flow inside the duct. Areas of higher flow velocity are created at the free vent surfaces and areas of low flow velocity and swirl at the grids. The flow profile steadies at a distance from the grid depending on the grid design but is usually 20 cm. For best accuracy, a large diameter vane is recommended. The area of the vane helps to get an average reading of the turbulent flow from the grid. Laminar flow in the centre of the duct Max. values Min. values Mean values Measurements at suction apertures using a volume flow funnel Even without the disturbing effects of a grid in an aperture, the lines of flow are not directional and the flow profile is irregular. Because a partial vacuum in the duct draws air out of the room in a funnel shape even a short distance from the aperture, there is no defined area in the room over which a measurement could be made. Therefore, only the duct or funnel measurement yields reproducible results. Measuring funnels of various sizes are available for such applications. These create defined flow conditions at a known distance from the grid with a fixed volume. A velocity probe is positioned centrally and secured. The volume flow is calculated from the velocity multiplied by the funnel factor (e.g. funnel factor 22). Measuring ambient air velocity using testo 400 in accordance with DIN 1946 Part 2, ANSI/Ashrae Ambient air velocity is a very important parameter in the thermal comfort of people in rooms. testo 400 supplies the current and mean air velocities. The maximum permissible mean air velocity depends on the air temperature measured by testo 400 and the amount of turbulence calculated from the air velocity. The example shows a permissible mean air velocity of 0.26 m/s with an air temperature measured at 24.4 C and an automatically calculated degree of turbulence of 10%. Ambient air velocity Mean air velocity m/s Air temperature in F Air temperature in C Degree of turbulence T 0% 10% 20% 40% 60% Mean air velocity fpm Measuring volume flow with a funnel Funnel x m/s v m 3 h = x m/s * 22 m 3 /h v = Volume x = Velocity 22 = Funnel factor Velocity probe

8 125 Pitot tube The Pitot tube opening takes on the complete pressure and conducts it to connection (a) in the pressure probe. The pure static pressure is taken up by a lateral slot and conducted to connection (b). The resulting differential pressure is a dynamic flow-dependent pressure which is then analysed and indicated. Total pressure Static pressure Static pressure Total pressure As with thermal probes, the Pitot tube is more likely to react to turbulent flows than a vane probe. Therefore, a free inlet and outlet path must also be ensured during Pitot tube measurements. a Pitot tube factor: s = 1.0 s = 0.67 b v = s 2 p ρ v = Velocity in m/s s = Pitot tube factor ρ = Air density in kg/m 3 p = Differential pressure in Pascal measured in Pitot tube Absolute pressure offset Measuring errors occur often because a mean density of 1200 g/m 3 is used in calculations. When measuring outer air flows, the actual air density can deviate by up to ± 10% from the given mean value. Therefore an inaccuracy in the air flow of up to ± 5% can result. Memory Location Probe Special Instr. Print Language The correct air density can be easily input in testo 400 The testo 400 can compensate for this by activating an automatic conversion for the Pitot tube pressure to velocity. Multipoint averaging can then be carried out directly in m/s values. Main menu Special Parameter Density factors MemoryParameter Location Pitot tube factor Probe Special Instr. Print Language Barometric pressure Absolute pressure in the duct D E N S I T Y Memory Location Parameter Temperature Probe Pito Humidity Special abs. Press. Metre a.s.l. Instr. Barom. pressure Print Diff. pressure Language Metres above sea level Temperature It is important that the correct air humidity is input in the configuration menu or that you measure absolute pressure, temperature and humidity with the absolute pressure probe and a temperature/humidity probe. testo 400 automatically calculates density on the basis of the measured values. Humidity Density Temp C Humidity 50.0 % abs. Press. 911 mbar g/m 3 M E A S U R E M E N T T E C H N O L O G Y

9 126 Assessment of VAC systems on location The VAC module option was developed for testo 400 to carry out quick and rational assessment of VAC systems. This new option carries out measurements on site quickly and efficiently and automatically provides printouts. Inaccurate data calculations as well as the time consuming entry of date and time are eliminated with testo 400. testo 400, with its VAC module, is currently the only measuring system worldwide with which a quick and objective assessment of the functionality of a ventilation system can be carried out. Evaluations can be carried out without any additional calculations. The measurement stipulations are based on internationally recognised standards; VDI 2080 in Germany, Euronorm (EN) 12599/ Draft and Ashrae standards in the US. Protocol 14 for test report no.: Grid measurement according to VDI 2080, DIN EN / 0998 Object: VAC system: Jones Ltd. Center K: 2m/s (MIN: 7.80 / MAX: 13.10) Ventilator rpm: 500 rpm Starting time: :14:05 Responsible: Manfred Schulze Finishing time: :14:20 The velocity measuring instrument knows the duct dimensions Easy preparation of measurement on location. All data related to the measurement location are entered, prior to the measurement, in your testo 400 via PC. All you have to do on site is call up the current location to access the information available in testo 400. The measurement results are saved in the location name selected by you. The volume flow is calculated using the duct data saved in the instrument. Settings /Grid measurement Duct cross section Duct (x) Duct (x) Duct (x) Duct (x) Duct (x) Duct (x) Duct (x) Duct (x) Duct (x) Duct (x) Date: Page 1/1 Geometrical data Accuracy Round Square Rectangular Area Long side 1.00 m Lateral side 2.00 m Area 2.00 m2 Correction factor 1.00 OK Cancel Space for your company logo Duct cross-section Mean value with min/max Measurement stipulation integrated User-guided processing of measurement stipulation in accordance with standard. The measurement points are displayed in testo 400. testo 400 assigns the respective coordinates in the duct to the selected measurement point. 1/1 (H 250 / V 500 mm) x Meas. pts specified by measurement specification + Selected measurement point x Previously measured measurement point Assessment of overall uncertainty on location Overall uncertainty is made up of the irregularity of the velocity profile, location inaccuracy, inaccuracy of the duct dimensions, accuracy of the velocity measurement system used and the number of measurement points. testo 400 takes all of these influences into consideration. In this way, the overall uncertainty of the measurement can be assessed directly on location. Instrument: Probe: testo 400 Pitot tube Ref. instruments: No calibration data included Last calibration: Title: Müller_12.345/8 Comment: Ref value 50,000 m3/h, 22 C, center, exhaust Duct dimensions: x (m) Meas. area: (m2) Grid: 4 x 4 Meas. points: 16 Hydr. diam.: (m) Meas. point m/s Distance (mm) a Measurement points with coordinates and mean value Mean m/s m3/h b c d Means of quadrants 1 2 Mean Profile irregularity: % 17.0 Uncertainty of location: % 7.8 Condition of outside air Air pressure pa: 950 hpa Temperature ta: 27.4 C Humidity RHa: 45.0 %RH Conditions in duct Abs.pressure: hpa Settings/T400 Temperature: 22.0 C Humidity: 35.0 %RH Uncertainties: Uncertainty of air density: g/m3 1 Accuracy of duct dimensions: mm 2 Date: Name: M. Spencer Volume flow: m3/h Uncertainty (abs.): m3/h Uncertainty (rel.): 8.9 % Air density: g/m3 Mass flow: kg/h Standard volume flow: M3/h(N) Uncertainties/Meas. system: Instrument accuracy: digit 1 Probe accuracy: m/s 0.40 Signature All values marked with colour are automatically accepted by testo 400 Printout of measurement results in standard layout The PC software uses all of the relevant data in testo 400 and shows them in the measurement protocol for each individual location. Time-consuming entry of all the readings and other parameters are thus eliminated. Processing of the measurement protocols is made much easier and quicker.

10 Industrial calibration: Velocity 127 Industrial calibration One basic requirement for calibrating velocity measuring instruments is a defined air stream. Calibration takes place in the centre of a free jet in a specially developed wind tunnel using the most accurate and efficient measurement method currently available, Laser Doppler Anemometry (LDA). LDA is a non-contact - therefore flow-free - measurement procedure used in ranges with low mm/s flow velocity at high accuracy levels. The laser beam is split into two parallel beams using a beam splitter. A lens is used to make an intersection. The intersection volume is right in the centre of the free jet. The measurement volume as an intersection of two jets is crossed by a lightdark strip (similar to a light barrier) which develops on account of the interference from the two jets which cross each other. Tiny particles of between 1 and 5 µm in size are added to the flow. When a particle crosses the light barrier, light is dispersed in all directions. One part of the light is focussed and registered on a photodiode using a receiving lens. When a particle goes through the light barrier system, a series of scattered light pulses is developed whose frequency is converted into particle or flow velocity. An average of approximately 50 particles per second fly through the light barrier system. Each particle emits approximately one flash per micro second (at 4 m/s). If there are approximately 30 light barriers in the measurement volume of the laser beams, the signal generator of the LDA systems has to process approximately 1.6 million flashes in one second. A modern LDA system carries out this calculation in the space of a few seconds at highest accuracy. Calibration in Testo s DKD wind tunnel The first PTB accredited laboratory for velocity enables the retraceable calibration of anemometers. Extract from the accreditation range of the DKD laboratory Parameter or Measurement range Measurement conditions Measurement item to be calibrated inaccuracy Flow velocity of 0.1 m/s to 50 m/s With free jet calibrated by 0.5 %; but not less gases Laser Doppler than 0.01 m/s Calibration of Anemometer anemometers C A L I B R A T I O N