Mine is bigger than yours: Shop A/C notes

On Aug 7, 9:09 pm, "Proctologically Violated=A9=AE"

It was really the Brits versus the Yankees. The Brits wanted the temperature to be lower. Warm beer after working in a cold shop. The Americans like cold beer after working in a warm shop. Makes sense to me.

Dan

John:

Outside of industrial metrology it's all over the map.

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In chemistry and other sciences, STP or standard temperature and pressure is a standard set of conditions for experimental measurements, to enable comparisons to be made between sets of data. Internationally, the current STP defined by the IUPAC (International Union of Pure and Applied Chemistry) is an absolute pressure of 100.00 kPa (1 bar) and a temperature of 273.15 K (0 °C).[1] Other organizations have established a variety of alternative definitions for the standard reference conditions of temperature and pressure, such as the SATP amongst others.

In industry and commerce, it is necessary to define the standard reference conditions of temperature and pressure when expressing a gas volume or a volumetric flow rate because the volume of a gas varies with the temperature and pressure of the gas. The available data on the various definitions of standard reference conditions clearly indicates that the IUPAC's STP is not a universally accepted definition of the standard conditions of temperature and pressure. For that reason, simply stating that a gas flow rate is 10,000 m³/h (i.e. cubic meters per hour) at "standard conditions" or at "STP" has no meaning unless the reference conditions that were applied are clearly stated.

In aeronautics and fluid dynamics the term "International Standard Atmosphere" is often used to denote the variation of the principal thermodynamic variables (pressure, temperature, density, etc.) of the atmosphere with altitude at mid latitudes.

Definitions in current use

There are a great many different definitions of the standard reference conditions currently being used. Table 1 presents twelve such variations of standard condition definitions - and there are quite a few others as well.

As shown in the table, the IUPAC (International Union of Pure and Applied Chemistry) currently defines standard reference conditions as being 0 °C and 1 bar (i.e., 100 kPa) of absolute pressure rather than the 1 atmosphere (i.e. 101.325 kPa) of absolute pressure used in the past. In fact, the IUPAC's current definition has been in existence since 1982.[2]

As further shown in the table, the oil and gas industries have to a large extent changed from their past usage of 60 °F and 14.696 psia to their current usage of 60 °F and 14.73 psia. This is especially true of the natural gas industry in North America.

For the SATP used in presenting chemical thermodynamic properties (such as those published by the National Bureau of Standards as included in Table 1) that the pressure is standardized at 1 bar (100 kPa) but the temperature may vary and needs to be specified separately.

It should also be noted that the International Organization for Standardization (ISO), the United States Environmental Protection Agency (EPA) and National Institute of Standards and Technology (NIST) each have more than one definition of standard reference conditions in their various standards and regulations.

The table makes it quite obvious that it is absolutely necessary to clearly state the temperature and pressure reference conditions whenever expressing a gas volume or gas volumetric flowrate. It is equally important to state whether the gas volume is expressed on a dry basis or a wet basis. As noted in the table, some of the current definitions of the reference conditions include a specification of the percent relative humidity (% RH).

Table 1: Standard reference conditions in current use

Temperature Absolute pressure Relative humidity °C kPa Publishing or establishing entity

Notes:

IUPAC: International Union of Pure and Applied Chemistry NIST: National Institute of Standards and Technology ISA: ICAO's International Standard Atmosphere ISO: International Organization for Standardization EEA: European Environment Agency EGIA: Electricity and Gas Inspection Act (of Canada) EPA: United States Environmental Protection Agency SATP: Standard Ambient Pressure and Temperature CAGI: Compressed Air and Gas Institute SPE: Society of Petroleum Engineers OSHA: U.S. Occupational Safety and Health Administration SCAQMD: California's South Coast Air Quality Management District OPEC: Organization of Petroleum Exporting Countries EIA: U.S. Energy Information Administration Std. Metro: U.S. Army's Standard Metro (used in ballistics) ==================================================================

See you have dealt with a few of "those" types in your time....lol,

Tom

Standard Temp in scientific calculations is 59 degrees F.

John

It doesnt pay to go to college and learn anything any more. They keep on changing the rules. :(

John

John:

Sometimes.

I read your prior post and poked around a bit. No wonder the American auto industry is so screwed up.

John:

They ought to put all the presidents of the standards organization in a big octagon and let them fight it out... winner sets the standards for everyone. LOL

Wonderful! Except Cliff isn't French...

The commonly given reason is that, in addition to being a comfortable working temperature in a toolroom, 20.0000 C and 68.0000 F are the same temperature no matter how many zeroes you tack on. The French and the English both get a round number.

I recall the first time I went to an American calibration lab (in 1984). We were calibrating some kWhr meters because the Korean customer wanted calibration in an independent country before paying the $4m efficiency bonus on the power station project. The temperature in that lab was 23 degrees C and I nearly had a fit. A lot of negotiation went on about whether it was better to change the temperature of the lab to the 20 deg level we normally used and calibrated the meters at, or to keep their standards at their normal temperature. In the end we did the calibration at the higher temperature, but I wasn't happy.

A couple of years later I had improved our metering to the point that we used NPL for our calibrations, since we were using instruments for on-site tests that were as good as the secondary labs.

A while later we got an enthusiastic reception at the Indian NPL in New Delhi because our instruments were better than theirs in terms of traecabililty and we were effectively carrying out a transfer calibration of them rather than the other way round :-)

Mark Rand (in the UK) RTFM

Do you know how mechanical electric usage meters measure true power if there is a large phase shift between current and voltage, in large capacitive or inductive loads, or even electronic loads, such as in the new fluorescent ballasts?

Yes.

Always in the electric companys favor, you should know that PV . On mine I can watch the wheel go backwards when running the cnc lathes for 2 seconds, then it speeds up forward. Go watch when your mill is changing speed.

Eddy currents are induced in the disk by the current coils of the meter, 90 degrees behind the phase of the current.

The voltage coil provides a magnetic field through the part of the disk where these currents are flowing. The voltage coil pole has a shorted turn winding around it that (theoretically) causes the field from this pole to lag the voltage by 90 degrees.

The currents in the disk and the field through the disk produce a torque that is proportional to the instantaneous product of the current and voltage... The true power.

Braking magnets cause a torque on the disk proportional to its speed, slowing it down.

The end result is that the speed of the disk is proportional to the power. Irrespective of power factor.

There are tuning resistors and shading plates to improve the accuracy at low power. Also, better grades of meters have much lighter movements and thinner disks to reduce variation with frequency and temperature changes.

It's really a wound rotor induction motor with a transformer providing the rotor current and a brake that is proportional to rotor speed.

Don't know if that helped at all, but if you take that explanation and use it when looking at a single phase meter, it may be of use.

Mark Rand RTFM

Wound rotor? Watt-hour meters I've seen have rotating discs with no windings on them.

Wound rotor in the sense that the current in the disk, that the voltage coil field interacts with, is produced by transformer coupling from the current coils. It's a wound rotor with a one-turn winding and a transformer rather than sliprings.

Trying to get across the concept that force=field x current x length and that the current in the disk is generated by one set of coils and the field is generated by the other set.

Or wound rotor as opposed to squirrel cage motor, where the rotor current is due to the rotor moving relative to the magnetising field.

Regards Mark Rand RTFM

OK, I see your point. Rotor eddy currents are not produced by the field that produces the torque (voltage coil field) but by a separate excitation means (current coils), while rotor currents in a squirrelcage rotor (hence torque) are due to slip speed. I guess the key difference is that generated torque is proportional only to the vector product of the field strengths, and not to rotor speed. Speed is then determined by where this generated torque is balanced by speed-proportional drag torque from a permanent magnet.

That's what I was trying to get at.

If I'd have been any good at explaining things in writing, I'd have been an author. If I'd have been any good at getting people to understand what I meant, I'd have been a manager.

I'm Neither

regards Mark Rand RTFM