AMAZON multi-meters discounts
AMAZON oscilloscope discounts
You are assigned to convert a machine
that operates with relay logic so that it will operate on solid-state
gates. Your supervisor will provide the original ladder logic diagram
of the machine for you. (See ill. 1 below.) When you have completed
converting the machine to solid-state gates, you should turn on
the power to the sys tem and test each input switch to determine
that the output for the logic is correct. You should also be able
to explain the parts of the circuit that may remain in control
of relay logic where the relay provides an advantage over the solid-state
gate. AMAZON multi-meters discounts
AMAZON oscilloscope discounts
|
![](images/1-20.jpg)
Above: Fig 1.
The solution to this job assignment should refer to the
relay ladder-logic diagram shown in ill. 1 (above) and the solid-state
logic circuit diagram shown in ill. 2 (below). This circuit is for the
bin-level control system that controls the filling of the bin when it
gets empty. Your solution should begin by identifying all the inputs in
the relay logic and all of the conditions for the circuit. Each condition
will be represented by a logic gate. If the relay logic contacts are in
series, an AND gate will be used; if the relay contacts are in parallel,
an OR gate should be used.
Above: Fig 2.
When you test the circuit, you should test each input with a logic probe
to determine that its signal will go HI and LO. Next you should set all
inputs to the proper signal to activate the logic. Test the output of the
logic gate to determine that it has the proper signal. If you use any amplifiers
or inverters, be sure to test them for the proper signal.
Refer to the table below to determine the strengths the relay provides
that would better suit it for the job than the solid-state logic device.
One reason to keep the relays is where amplification is required to get
a small signal from the solid-state circuit to a level where it can energize
or de-energize 110 volts ac devices.
Strengths of solid-state devices
- fast
- inexpensive
- small size
- reliable up to 5 million cycles
- encapsulated, good in explosive environment
- some circuits modularized or in socket for easy replacement
Weaknesses of solid-state devices
- difficult to troubleshoot some devices soldered
- require power supply
- some CMOS susceptible to static
- don't tolerate heat well
- may need fan or air conditioning
- small-signal voltage picks up noise
- must be mounted near inputs because of low voltage
Strengths of relays
- easy to change out
- durable
- easy to test
- available with plug-in base
- miniature relays available
- immune to noise
- 110 volts signals allow relays to be mounted further from
inputs
- maintenance personnel already familiar
Weaknesses of relays
- contact wear
- moving parts (springs) limit life expectancy from 1-3 million
cycles
- require more power than solid-state devices
|
|