Similar to STP, only the assumption uses standard temperature as 32°F (0°C) and 14.696 PSI (1 Bar). Any unit of measure beginning with an “N” indicates that flow meter needs to operate at Normal conditions to be accurate.
Standard Temperature and Pressure. A base value used for pressure and temperature in calculations that are dependent upon these variables. Because these values can vary depending on conditions, an assumption of 68° F (20°C) and 14.696 PSI (1 Bar) is used for calculations. An “S” at the beginning of any unit of measure (i.e. SLPM, SCFH) indicates that the flow meter was made assuming STP, and will only read accurately when used at STP as well.
Pounds per square inch gage. The amount of force applied to any object. Uses atmospheric pressure as a relative zero baseline. Because most everything in the world is subject to Atmospheric pressure, measurements sometimes ignore this value and only measure the additional forces applied to objects.
Pounds per square inch absolute. The sum of Atmospheric pressure (14.696 PSI) and any additional pressure forces. Atmospheric pressure is the amount of force we experience in everyday life. Although we do not feel this force, there is a constant force of 14.696 pounds per square in acting on us.
The ability of the flow meter to read a given flow rate the same every time when a common set of parameters are applied.
The ability to read a flow rate, not specifically called out on a flow meter. For example the ability to see 1 LPM mark on a flow meter with 100 LPM as a maximum, is much more difficult than if the maximum flow rate were only 10 LPM. Resolution could also could be defined as the value of each intermediate marking on a flow meter. With an increasing maximum flow rate, each intermediate flow rate has an increasing value, therefore decreasing the resolution of the intermediate points.
The effective measurement range of the flow meter; or the ratio of maximum flow value to the minimum flow value. For example, if the maximum stated flow rate on a meter is 100 LPM, a 10:1 turndown will allow the minimum flow rate to be 10 LPM. If the turndown were 100:1, the minimum flow rate would be 1 LPM.
The lagging of a reaction from the initial cause. For example, with flow meter valves, there is a slight Hysterisis. When a valve is opened, the increase in flow may lag slightly behind the actual movement of the knob.
- Turbulent Flow
Fluid flow (air & water & gases) flowing in random, mixing motion. This flow will not remain in layers; rather it flows within adjacent layers.
- Variable Area Rotameter
The principle of operation for most of Key Instruments flow meters. The design consists of a “float” in a vertical, tapered tube. As flow enters the bottom of the tube, it raises the float proportionally to the flow rate. As the flow rate is increased, the float moves upward increasing the area for passage of fluid. When the upward force of the fluid is equal to downward force of float it will reach an equilibrium position.
- Parallax Line
A second line added to a flow meter to prevent an incorrect flow measurement made based on a line of sight that is not perpendicular to the flow meter. In order to use the parallax a user will line up the desired measurement line with that lines corresponding line on the rear of the meter. This will ensure a measurement is accurate and repeatable.
- Specific Gravity
The ratio of a mass of liquid to an equal mass of water. Also, the ratio of a volume of gas, to an equal volume of Air. This comparison needs to be done at the same prescribed temperature and pressure. The ratio is used to design flow meters for gases other than air; and liquids other than water.
The resistance of a liquid to flow. For example, Molasses has a much higher viscosity than water and will not flow out of a container as easily as water.
- Percent of Full Scale
Accuracy tolerance that is determined by taking a percentage of the maximum flow rate (full scale value)
– For example, if you are reading 5 LPM on a 10 LPM meter with an accuracy of ± 5% full scale: ?± 5% full scale = 0.5 LPM?. Making the reading of 5.0 LPM to be in the range of 4.5 LPM to 5.5 LPM.
- Does a meter have to be mounted vertically?
Yes, and No. All standard products have been designed to work when mounted vertically. To maintain stated tolerances, flow meters need to be mounted vertically. However, Key Instruments can design a flow meter that can be mounted at any desired angle!
- Pressure Drop
Is the loss of pressure between two points. This is associated with the resistance a gas or liquid experiences while flowing through a flow meter. In most flow meter applications, if an inlet pressure of 50 PSI is used for example, the pressure at the outlet of the flow meter will not be exactly 50 PSI. There are many things that can affect the flow meters pressure drop. Piping that is too small to handle the amount of volume of liquid or gas through a flow meter, piping that is too long, and too many curves and bends in piping can all cause excessive pressure drop.
- NIST Traceable
National Institute of Standards and Technology Traceable.?This means that all gages and equipment used in the manufacturing, assembly, and testing of Key Instrument products have been compared and calibrated against a national standard.
- FDA GMP
Food and Drug Administration “Good Manufacturing Practices”. This serves to indicate that Key Instruments actively maintains a quality control system for the design, manufacture, packaging, labeling, storage, installation, and servicing of finished medical devices intended for commercial distribution in the United States. This is a set of requirements set forth by the FDA, and shows our commitment to provide the highest quality product possible.
Certificate of Conformance. This is a document that can be supplied with any product that will verify the product you are buying has been manufactured, assembled, and tested to all agreed upon parameters as stated in the Purchase Order, technical drawings, and engineering related materials. It’s your reassurance that what you ask for is what you are receiving.
- Primary Standard
Primary standards are directly traceable to the National Institute of Standards and Technology (NIST)?. Key Instruments offer a 10-point calibration with NIST traceable certificate.
- Secondary Standard
Secondary standards are calibrated by reference standards traceable to NIST.? Products are flow checked using secondary standards before they are shipped.
- Volumetric Flow
The rate at which a volume of a fluid is flowing or has flowed
- Definitions of Units
- CCM – Cubic Centimeters per Minute
- LPM – Liters Per Minute
- LPH – Liters Per Hour
- CFM – Cubic Feet per Minute
- CFH – Cubic Feet per Hour
- GPM – Gallons Per Minute
- GPH – Gallons Per Hour
- How do you read a float?
The float in any Key Instruments Flow meter is read at the lowest and largest diameter on the float. See examples below. For a spherical float, the flow rate is read at the center of the ball. For cone shaped floats, a key is printed on all meters to show where to measure. In general this point is the lowest and largest diameter on the float.