EBK MINDTAP FOR HERMAN'S UNDERSTANDING
4th Edition
ISBN: 9781337798761
Author: Herman
Publisher: VST
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Textbook Question
Chapter 39, Problem 1RQ
Why are NEMA symbols such as push buttons, float switches, or limit switches not used in programmable logic controller schematics?
Expert Solution & Answer
To determine
Identify why the NEMA symbols for components such as push buttons, limit switches and float switches are not used in the schematic of a programmable controller.
Explanation of Solution
The programmable logic controller can only recognise whether a contact is open or closed. It doesn’t know if the contact is connected to components such as float switches, push buttons and so on.
Thus, there is no NEMA symbol used to identify components such as push buttons, limit switches and float switches in the schematic of a programmable controller.
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Example 8: 900 Kg dry solid per hour is
dried in a counter current continues dryer
from 0.4 to 0.04 Kg H20/Kg wet solid
moisture content. The wet solid enters the
dryer at 25 °C and leaves at 55 °C. Fresh
air at 25 °C and 0.01Kg vapor/Kg dry air is
mixed with a part of the moist air leaving
the dryer and heated to a temperature of
130 °C in a finned air heater and enters the
dryer with 0.025 Kg/Kg alry air. Air leaving
the dryer at 85 °C and have a humidity
0.055 Kg vaper/Kg dry air. At equilibrium
the wet solid weight is 908 Kg solid per
hour.
*=0.0088
Calculate:- Heat loss from the dryer and
the rate of fresh air.
Take the specific heat of the solid
and moisture are 980 and 4.18J/Kg.K
respectively,
A. =2500 KJ/Kg.
Humid heat at 0.01 Kg vap/Kg dry=1.0238
KJ/Kg. "C. Humid heat at 0.055 Kg/Kg
1.1084 KJ/Kg. "C
2.8
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العنوان
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Jon
14.23. A double-effect forward-feed
evaporator is required to give a product
consisting of 30 per cent crystals and a
mother liquor containing 40 per cent by
mass of dissolved solids. Heat transfer
coefficients are 2.8 and 1.7 kW/m² K in the
first and second effects respectively. Dry
saturated steam is supplied at 375 kN/m²
and the condenser operates at 13.5 kN/
m².
(a) What area of heating surface is
required in each effect assuming the
effects are identical, if the feed rate is 0.6
kg/s of liquor, containing 20 per cent by
mass of dissolved solids, and the feed
temperature is 313 K?
(b) What is the pressure above the boiling
liquid in the first effect?
The specific heat capacity may be
taken as constant at 4.18 kJ/kg K. and
the effects of boiling-point rise and of
hydrostatic head may be neglected.
Chapter 39 Solutions
EBK MINDTAP FOR HERMAN'S UNDERSTANDING
Ch. 39 - Why are NEMA symbols such as push buttons, float...Ch. 39 - Prob. 2RQCh. 39 - Why are normally closed components such as STOP...Ch. 39 - Prob. 4RQCh. 39 - Prob. 5RQCh. 39 - List four basic rules for developing a program for...Ch. 39 - A PLC requires that times be programmed in...Ch. 39 - When programming in Boolean, what statement should...Ch. 39 - When programming in Boolean, what statement should...Ch. 39 - In a control circuit, it is imperative that a coil...
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