- 1 Packing Liquid
- 2 Installation
- 2.1 High-Pressure Gas Meters (> 1 bar)
- 2.2 Positioning
- 2.3 Filling with the packing liquid
- 2.4 Adjusting the packing liquid level
- 2.5 After filling and adjustment of the packing liquid
- 2.6 Grounding of Gas Meters made out of electrically conductive material (stainless steel or PE-el)
- 2.7 Connection of gas pipes
- 2.8 Moving of the filled meter
- 3 Measurement
- 4 Maintenance
The meter must be filled with the same packing liquid which the meter was calibrated with. Otherwise major measurement errors will occur!The Gas Meter (which is shipped dry) must be approximately half-filled with a suitable »Packing Liquid« before first use. The measuring drum which rotates in the packing liquid forms the actual measuring unit in conjunction with the liquid.
The packing liquid has two functions: Firstly, it seals off the active measuring chamber (inside the measuring drum which is being filled with gas). Secondly, the packing liquid level inside the measuring chamber defines the volume of the measuring chamber. The latter function is the basis for calibration of the gas meter’s measurement accuracy which is performed at the factory. Therefore, the measurement accuracy is directly dependent on the packing liquid level and so an incorrectly set level at time of installation is bound to cause incorrect measurements (see »Adjusting the packing liquid level«).
Mutual influence of packing liquid and gas
Irrespective of the chosen packing liquid, the packing liquid and the flowing gas inevitably affect each other with respect to evaporation and dissolving:Generally valid figures and limit values for the mutual influence of gas and packing liquid cannot be stated, because they depend to a great extent on the particular gas and its state. For example, when water is used as a packing liquid, a dry, warm gas absorbs significantly more evaporated water particles than a moist and cool gas. The solubility of gases in the packing liquid also varies greatly. The gas can only dissolve in the packing liquid up to the saturation limit. A measuring error caused by solubility can be avoided if the gas can dissolve in the packing liquid up to the saturation limit during test operation before the experiments are subsequently carried out.
Selection of packing liquidThe criterion for choosing a packing liquid should be that any mutual influence between the packing liquid and the flowing gas should be as small as possible, or that the effects can be ignored. In most cases, water can be used as the packing liquid. No special requirements for the water are necessary – that means that normal clean tap water can be used. When water is not suitable as packing liquid, oils or synthetic liquids can be used. Generally speaking, a thin-bodied fluid (ideal: viscosity of water) with a low vapour pressure (ideally: < 0.1 mbar/hPa) should be selected. A thin-bodied fluid causes a small friction resistance of the rotating measuring drum only, and hereby a small pressure difference between gas inlet and outlet of the meter. This results in a better (flatter) calibration curve. A low vapour pressure reduces the (unavoidable) evaporation of the packing liquid. A better long term stability of the packing liquid level is obtained and thus more stable measuring results.[/wpml-string]
RITTER recommends and can supply the following packing liquids:
High-Pressure Gas Meters (> 1 bar)
PositioningPlace the Drum-type Gas Meter onto a solid, vibration-free support. Align the gas meter precisely horizontally by means of the integrated level (at top of casing) and the levelling feet.
Filling with the packing liquidIt is essential to use the same packing liquid which the gas meter was calibrated with. The packing liquid is stated on the calibration certificate as well as at the calibration label on the Gas Meter.
Using a different packing liquid other than that used with the calibration will cause a significant measuring error!
Standard-pressure Gas Meters:
High-pressure Gas Meters:
Adjusting the packing liquid levelThe amount of packing liquid depends on the size/type of the Gas Meter and on the individual setting for each unit. The approximate quantity is shown in the data sheet enclosed with every Gas Meter. This quantity does not take into account individual differences based on the calibration performed in the factory.
Fine adjustment of the packing liquid level is essential for measurement accuracy, since the measurement accuracy/display depends directly on the packing liquid level and reacts very strongly to an incorrectly set level!
For Gas Meters with the standard Packing Liquid Level Indicator (located at the rear plate of the Meter):When the Packing Liquid Level Indicator (1) is opened by turning the sealing screw (2) with Plastic Meters (or stop cock (2) with Stainless Steel Meters), the rising pipe of the level indicator is connected to the packing liquid in the Gas Meter housing in accordance with the communicating pipes principle. When the level in the Gas Meter housing rises when filling with packing liquid, the level in the level indicator rises accordingly. The correct packing liquid level is reached when the surface of the liquid column in the level indicator is flush with the upper edge of the level indicator (3) and neither forms a convex or concave shape (figure 2).
After filling and adjustment of the packing liquid
Grounding of Gas Meters made out of electrically conductive material (stainless steel or PE-el)Gas Meters with a casing and/or measuring drum made out of electrically conductive material (stainless steel or PE-el) must be grounded in order to discharge a potential static charge. For this purpose, the feeder clamp at a flange screw of the meter’s rear plate must be connected to ground (earth).
Connection of gas pipes
Connect the gas pipe to the inlet nozzle marked »gas inlet« at the rear plate. Allow the meter to perform one or two revolutions in order to remove any possible air bubbles within the measuring drum. Then disconnect the gas pipe again and repeat the steps from: »Filling with the packing liquid« and »Adjusting the packing liquid level«.
Moving of the filled meterIf the Gas Meter has to be moved after having been filled (for example carried into another room), it must be kept in a horizontal position. This is to avoid packing liquid getting into the gas inlet. If this occurs, the Gas Meter should be tipped 90° forwards (until the dial faces the floor). The packing liquid can then drain out of the gas inlet again (and back into the Meter).
Determination of Flow Rate
Due to their design, Drum-type Gas Meters measure the volume of flowing gases and indicate the measured volume by means of a needle and counter. A flow rate cannot be measured directly and must be calculated via the measured volume per time unit. This can be done by software or external hardware. For this purpose RITTER recommends these products: Data Acquisition Software »RIGAMO« and Electronic Display Unit »EDU 32 FP«. Note: For both options, the Gas Meter must be equipped with a Pulse Generator.
When graphing a calculated flow rate, the corresponding curve will not be linear but wavy, even if the original gas flow rate was constant. This is physically unavoidable due to the design principle of Drum-type Gas Meters:The measuring drum of the drum gas meter consists of four individual chambers that are opened and closed cyclically. The preceding chamber must be closed before the following chamber opens. This »forced measurement« is the reason for the high measuring accuracy of Drum-type Gas Meters, on the other hand, the opening/closing causes a slight pressure change inside the chamber. Furthermore, the surface tension of the packing liquid used causes an increase in pressure when a measuring chamber emerges from the liquid. The resulting pressure change causes a change in the rotational speed of the measuring drum, which causes the described wavy curve of the volume flow. This effect is called »periodic error of drum-type gas meters«. The smaller the Gas Meter, the greater the effect: for a TG05 the effect can be ±20 – 30%. The effect is avoided when using integer drum revolutions as a time base for the volume flow calculation. The Data Acquisition Software »RIGAMO« can be parameterised to calculate the volume flow using integer drum revolutions and avoid any periodic error. With the Electronic Display Unit »EDU 32 FP«, the volume flow is calculated by means of a moving average, which reduces the periodic error.
Initial set-up of measurementTo simplify the readout at the end of measurements, the large needle of the dial plate can be set manually to zero prior to each measurement. For units equipped with a totalizing roller-type counter (standard version), noting the counter reading is necessary. With a resettable roller-type counter (optional), the counter can be set to zero with the reset button. The Gas Meter is now ready for operation.
Examination of packing liquid level
Review of performance dataWhen taking measurements, the performance data of the respective Gas Meter (refer to the attached data sheet) must be observed. The maximum pressure load is 50 mbar for standard Drum-type Gas Meters made from plastic and 500 mbar with Meters with a stainless steel casing.
Measurements with oxygenThe mixture of some gases with oxygen can cause explosive reactions. Therefore, before and after measuring with oxygen, ensure that no gas used in the previous measurement is still within the measuring drum or the inside the housing. To minimize the danger of explosion, the Gas Meter has to be purged with an inert gas (e.g. nitrogen or any noble gas). This can be performed by operating the Gas Meter with an inert gas for at least five revolutions of the measuring drum (= five revolutions of the large needle on the dial plate).
GeneralAll RITTER Drum-type Gas Meters are maintenance-free. Additionally, no leakage from the Gas Meter casing can occur by use of a magnetic coupling between measuring drum and counter mechanism.
Cleaning of casing and measuring drum from sedimentsWhen the measured gas carries particles, these particles will be scrubbed by the packing liquid and the rotation of the measuring drum during the measuring process. Thus, sediments may build-up at the bottom of the casing and inside of the measuring drum over the time. In order to clean the casing and measuring drum from these sediments, the casing should be flushed from regularly. This requires draining the casing through the drainage faucet. Refill the Meter with clean water and add any detergent (if appropriate: dishwashing detergent) which does not attack the meter material. Repeat draining and refilling until no sediments are visible while draining the Meter. If the Gas Meter is small enough, it is recommended to hold the meter »face down« and to shake the meter slightly when coming to the end of the draining process. Thus, potential sediments at the inside of the measuring drum are scrubbed in the best possible way.
Disassembly of the rear plateThe rear plate of the housing can be removed in order to allow the Gas Meter housing to be cleaned from the inside if required. When removing the plate, it is essential to ensure that the support secured onto the inner face of the housing rear plate and which engages in the measuring drum is not broken off and that the measuring drum is not damaged by this support. However, after opening the Gas Meter housing and removing the measuring drum, please note that the measuring drum might no longer be in the same position as it was during calibration at the factory. This could result in a different calibration result. It is recommended returning the Gas Meter to the factory for inspection, cleaning and recalibration if the measuring drum becomes dirty and in the event of measuring inaccuracies or other operational malfunctions.
In the unlikely event of a malfunction of the Meter, please contact your national distributor or RITTER directly. In order to determine the cause of the malfunction quickly, please provide the following information when contacting support:
Rev. 2023-09-06 / Subject to alterations.
Dr.-Ing. RITTER Apparatebau GmbH & Co. KG · Coloniastrasse 19-23 · D-44892 Bochum · Germany
For questions please contact firstname.lastname@example.org or your local distribution partner (on our overview page)