Quantcast Microprocessor Instrumentation

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(g) An adjustable damping restriction permits making any adjustments
r e q u i r e d to dampen violent fluctuations and give a steady reading.  The
a d j u s t m e n t s can be made without interfering with the operation of the
flowmeter.
T h e types of recorders described in
paragraphs 3.1, 3 . 2 , and 3.3 are still be in use in many installations, but
t h e y are rapidly being replaced by recording instruments that are
m i c r o p r o c e s s o r driven.  E l e c t r o n i c sensors in the metering equipment transmit
s i g n a l s with the aid of amplifiers to strip chart recorders (figure 6-7) and
d a t a loggers (figure 6--8).  M i c r o p r o c e s s o r driven recorders are more accurate,
e a s y to calibrate, and safer than older mechanical traps.
The Btu meter is a special type of meter generally used in
3 . 5 Btu Meters.
H T W generating stations of more than 20 million Btu per hour output. The
m e t e r is used to integrate heat flow in the system.  One component of the
meter measures the instantaneous temperature difference between the flow and
r e t u r n l i n e s , usually recording these temperatures at the same time.
Simultaneously, another component. measures the instantaneous rate of water
f l o w in the return line, by means of an orifice or venturi tube. The Btu
m e t e r obtains the instantaneous products of the temperature difference and
f l o w , and integrates them.  T h e result of the multiplication and integration
is the heat energy delivered to the system, or removed by the heat consumer
across which the meter is connected.  The flowmeter component usually records
the flow at the same time.  B t u meters have also been electronically linked to
recorders  and  data  loggers.
4 CALIBRATION.  I t is important that the operator be cognizant of the scales
a n d ranges for which the gauges are calibrated. Typical calibrations follow.
q Pressure Gauges.
Pressure gauges and pressure recorders are generally
c a l i b r a t e d in pounds per square Inch (psi), inches of water (in. WG)
o r inches of mercury (in. Hg), depending on the pressure range and
k i n d of fluid being measured.
q Temperature Gauges.
Thermometers and temperature recorders are
u s u a l l y calib r a t e d in degrees Fahrenheit (F).
F l o w m e t e r s are ordinarily calibrated in pounds per hour
q Flowmeters.
( l b / h r ) , gallo n s per minute (gpm), or cubic feet per minute (cfm).
q Btu Meters.
B t u meters are usually calibrated in Btu's per hour.
q Instrument
Characteristics.  Instrument range should be such that
u n d e r normal conditions of operation, t h e I n d i c a t i n g p o i n t e r d i s p l a y
w i l l remain at midrange.  V a r i a t i o n s in operating conditions should
o c c u r within the middle third of the range.  Instruments should be
self-compensating and should not be affected by external changes in
t e m p e r a t u r e or pressure.
5 TELEMETERING.  Telemetering is used when the conditions of the installation
require a central supervisory control system.  This permits remote indication,
recording, and/or control of the system fluid conditions.
6-10





 


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