why is archie slow?

why is archie slow?

Post by Curt Finc » Wed, 25 Jun 1997 04:00:00



everytime i've ever used archie it is incredibly slow.

why is it the slowest search engine in town no matter
where the server is, who the client is, no matter what?

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why is archie slow?

Post by Ian Stirlin » Fri, 27 Jun 1997 04:00:00


Curt Finch <c...@journyx.com> wrote:

: everytime i've ever used archie it is incredibly slow.

: why is it the slowest search engine in town no matter
: where the server is, who the client is, no matter what?

Comparatively older technology, and less resources put into it
usually, often altavista or other search engines can find URL's
you can downloac things from.

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Ian Stirling.   Designing a linux PDA, see  http://www.mauve.demon.co.uk/
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   [INLINE]
     ___________________________________________________________

  Index

     ___________________________________________________________

                         The Thermocouple Effect

   It has been known for a long time (Seebeck, 1822) that a voltage
   exists across the junction of dissimilar metals. Figure 1 shows
   a thermocouple junction formed by joining two metallic alloys, A
   and B. The voltage across the thermocouple junction depends on
   the type of metals used and the temperature of the junction. The
   mechanism responsible for this voltage is quite complicated,
   however, there are certain phenomenological results which make
   the effect useful for measuring temperature.

   [INLINE] Fig. 1 Thermocouple Junction

   The first of these results is that the voltage is approximately
   linear with temperature. The change in junction voltage as a
   function of junction temperature is given by the equation :

   delta V = a x delta T

   where 'a' is the Seebeck coefficient. The magnitude of this
   coefficient depends on the metals used to form the junction:
   typical values range from 0 to 100 uV/C.

   Nonlinearities

   Unfortunately, the magnitude of the coefficient depends on
   temperature. It is generally smaller at low temperatures, and
   may change by more than a factor of two over the useful
   operating range of a thermocouple. Despite this non-linearity,
   the induced voltage is (usually) a monotonically increasing
   function of temperature, and the voltages generated by certain
   pairs of dissimilar metals have been accurately tabulated. These
   tabulated values are referenced to the voltage seen across a
   junction at 0 C.

   Additional Junctions

   A problem arises when measuring the voltage across a dissimilar
   metal junction - two additional thermocouple junctions form
   where the wires connect to the voltmeter (Fig. 2). If the wire
   leads which connect to the voltmeter are made of alloy "C", then
   there exist thermal emf's at the A-C and B-C junctions. There
   are two approaches to solve this problem: use a reference
   junction at a known temperature, or make corrections for the
   thermocouples formed by the connection to the voltmeter.

   Thermocouple Junctions Fig. 2 Additional Junctions

   Figure 3 shows the use of a "reference" or "compensating"
   junction. With this arrangement, there are still two additional
   thermocouple junctions formed where the compensated thermocouple
   is connected to the voltmeter. However, the junctions are
   identical (they are both junctions between alloys A and C). If
   the junctions are at the same temperature, then the voltages
   across each junction will be equal and opposite, and will not
   affect the measurement. Typically, the reference junction is
   held at 0 C (by an ice bath, for example) so that the voltmeter
   readings may be used to look up the temperature.

   Ice Bath Reference Junction Compensation Fig. 3 Reference
   Junction Compensation

   Compensation Without Reference Junctions

   The second approach to the problem relies on the fact that the
   voltage across the junction A-C plus the voltage across the
   junction C-B is the same as the voltage across a junction of
   A-B. As long as all the junctions are at the same temperature,
   the presence of an intermediate metal (C) has no effect. This
   allows us to correct for the voltage seen by the voltmeter in
   Figure 4 by measuring the temperature at the A-C and B-C
   junctions and subtracting the voltage which we would expect for
   an A-B junction (at the measured temperature). In the SR630 the
   temperature of the A-C and C-B junctions are measured with a low
   cost, high resolution semiconductor detector, and the subtracted
   voltage is the tabulated voltage of the A-B thermocouple at the
   measured temperature of the A-C and C-B junctions. The advantage
   of this method is that any type thermocouple may be used without
   having to change compensation junctions or maintain ice baths.

   Characteristics of Thermocouple Types

   Any two dissimilar metals may be used to make a thermocouple. Of
   the infinite number of thermocouple combinations which can be
   made, the world has standardized seven types which exhibit a
   range of desirable features. These thermocouple types are known
   by a single letter designation: J, K, T, E, R, S or B. While the
   composition of these thermocouples are international standards,
   the color codes of the wires are not. For example, in the USA,
   the negative lead is always red, while the rest of the world
   uses red to designate the positive lead. Often, the standard
   thermocouple types are referred to by their trade names. For
   example, K type is sometimes called Chromel-Alumel, which is the
   trade names of the Ni-Cr and Ni-Al wire alloys.

   It is important for a good thermocouple to have a large, stable
   Seebeck coefficient, wide temperature range, corrosion
   resistance, etc. Generally, each wire of the thermocouple is an
   alloy. Variations in the alloy composition and the condition of
   the junction between the wires are sources of error in
   temperature measurements. The standard error of thermocouple
   wire varies from 0.8 C to 4.4 C, depending on the type of
   thermocouple used.

   Voltage vs. temperature measurements have been tabulated by NIST
   for each of the seven standard thermocouple types. These tables
   are stored in the read-only memory of the SR630. The instrument
   operates by converting a voltage measurement to a temperature,
   with the internal microprocessor interpolating to achieve 0.1 C
   resolution.

   The K type thermocouple is recommended for most general purpose
   applications. It offers a wide temperature range, low standard
   error, and has good corrosion resistance. The K type
   thermocouples provided by SRS have a standard error of 1.1 C,
   half the standard error designated for this type.
     ___________________________________________________________

  Thermocouple Reference Data

Type                      B           E       J       K       R
 S            T

Positive Material         Pt/Rh(30%)  Ni/Cr   Fe      Ni/Cr   Pt/Rh(13%)
 Pt/Rh(10%)   Cu
Negative Material         Pt/Rh(6%)   Ni/Cr   Cu/Ni   Ni/Al   Pt
 Pt           Cu/Ni
Positive Color(USA)       Grey        Purple  White   Yellow  Black
 Black        Blue
Negative Color(USA)       Red         Red     Red     Red     Red
 Red          Red
Lowest Temperature        50C         -200C   0C      -200C   0C
 0C           -200C
Highest Temperature       1700C       900C    750C    1250C   1450C
 1450C        350C
Minimum Std Error         4.4C       1.7C   2.2C   2.2C   1.4C
 1.4C       0.8C

 
 
 

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