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MK 2015 GASOMETER TECHNICAL PUBLICATION
By Coleman Wood
Emdyne Gasmeter White Paper
Since the days of the Ancient Greeks, measuring the volume of solid, irregular objects relied on collecting the water displaced by immersing the object and then pouring that water into a calibrated rigid container to note the indicated volume. This classical method, the Wet Test Method, has long served to work well for solids, or liquids when poured into the calibrated container directly. However, any such apparatus for measuring the volume of a gas based upon liquid displacement inherently introduces errors that result from temperature, water-vapor contamination or compression of the collected gas. Compression effects can introduce significant volume measurement errors, especially when measuring higher molecular weight gases.
This paper addresses a novel means of measuring gas volume at very near atmospheric pressure, virtually eliminating compression induced errors, using a liquid-free design that differs notably from classical metering devices and methods used in scientific testing and experimentation laboratories over the years. This is a significant advancement for this field of metering that has wide applications including: Petrochemical core analysis, Educational chemistry and engineering departments, National laboratory advanced physical research,
Medical and pharmaceutical research and development studies, Environmental contamination and abatement studies,Aerospace/Defense research programs, and Manufacturing and quality control.
Although measuring gas volume is the primary purpose of the GASOMETER, it has also been used in combination with laboratory grade liquid metering pumps to measure and calibrate their flow characteristics. Another use can be as a calibration standard for flow meter manufacturing quality control. This versatile instrument can prove indispensable in standards testing laboratories and at calibrating assorted equipment for volume and flow rates precisely. The GASOMETER has been successfully employed to measure gases evolved from crude oil studies in laboratories worldwide since 1986.
How it Works
The GASOMETER employs a patented process utilizing a modern electro-mechanical mechanism coupled via digital/analog control circuitry to drive a linear motor/piston assembly bi-directionally. This method works to return a slight pressure increase, due to the introduction of a supply gas to be measured, back to local atmospheric pressure by advancing a piston within a cylinder accepting the gas sample. The advancing piston acts to promptly reduce the introduced gas pressure to atmospheric pressure, at which time the motor is commanded to stop. The sequence may be repeated indefinitely to collect unlimited volumes.
This process of advancing a piston into a cylinder to equalize the pressure of an incoming sample with atmospheric pressure may be thought of as the converse of positive displacement and requires a new term. ACTIVE ACCOMMODATION better describes the functioning of the GASOMETER and this method in metering gases can be considered a revolutionary improvement.
During motor shaft travel, high-speed pulses are generated and counted via a divider circuit to indicate volume of 0.1 cc at the finest resolution. An 8 digit electronic rate meter/count indicator displays the accumulated volume, provides for calibration scaling and delivers numerical data output via a rear panel serial port to a logging system, if desired. The backlit count indicator memory is non-volatile in the event of power disruption. A manual reset button is provided.
A key feature of the GASOMETER is its servo-based operation: By providing power assist to the collection/measurement process using a linear stepper motor moving two pistons on a common shaft, no energy is extracted from the incoming gas stream. This method permits an ultra-low (< 0.3 inches water-column) momentary pressure increase to activate the motor. In operation, the first of two cylinders is fed via a valve manifold the input gas to be measured until, at a volume of 200 cc, the operation reverses and the second cylinder becomes the active one for the next 200 cc. This operation may be repeated indefinitely at flow rates up to 30 liters per hour.
In contrast, generic Wet Test Meter volume indicators rely on the buoyancy of the measured gas to propel a rotating collection chamber that drives a gear train to move indicator needles that express volume collected. This method works by extracting energy from the gas flow opposing the back- pressure of an enclosed sealing fluid, usually water or special oil, in the measuring chamber to drive the gears.
Household natural gas meters, similarly, rely on relatively high gas main pressure to actuate flexible diaphragms that in turn drive the gears and indication dials displaying volume used by the customer. Both of these passively driven metering methods require a pressure difference and flow to operate, thus affecting the process being measured. In precision laboratory studies it is important for the measuring device to contaminate or modify the phenomenon under study as little as physically possible.
Contaminating a dry gas sample with water vapor also changes the measured volume of gas by a few percent. This must be corrected for numerically to represent the true volume of gas measured, with temperature being a significant factor. No such compensation is needed for the GASOMETER because the sample is not in contact with any liquids during collection and metering.
When calibrated precisely to the customer's laboratory volume standard, the GASOMETER provides dependable, repeatable volume measurements at a constant ambient temperature. Once allowed to stabilize at the laboratory's temperature, a balance adjustment is performed to maximize the pressure sensitivity of the instrument by using front panel controls. The motor/piston assembly is then indexed, the counter and alert LED are reset, and sample collection may begin. When a data logging system is desired, the rear panel RS-232 count and the temperature outputs are available singly or in combination.
The EMDYNE, Inc. MK 2015 GASOMETER, is featured in the August 2016 issue of Test and Measurement Tech Briefs under the New Product announcements on page 17. See http://info.hotims.com/61064-408, or http://emdynegasmeter.info for more information and photos.
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