Programming

1
Programming Interfacing Analog I/O Devices for
the Micrologix 1200 PLC

• Ms. Jacqueline E. Miley
• Dr. John R. Wright, Jr., CSIT
• Millersville University

http//www.electrolink.co.nz/CC256A1C0073A9F5/DCB5
30D95C0C8EBFCC2569280012C8A6/2EF1809B80DFE3F8CC256
A1C0082CEBB!Open
2
Hybrid MicroPLCs as an Advanced Control Solution

• Historically, PC based systems controlled a
  process by using a PLC to handle the critical
  real-time I/O and discrete logic, while the PC
  took care of the analog PID loops and HMI
  functions (Merritt, 2000).

According to Omrons Mr. Cummings, another key
to the PLCs success in the face of competition
from PCs is the PLCs ability to be closely
scaled to the application. Increased
price/performance of the small, microPLC with
increased functionality previously only found in
large, rack mounted PLCs, will make the this
category of PLC very attractive for small
applications. To achieve this flexibility, users
can replace many large PLCs by distributing
control to smaller PLCs and networking them
together (Staff, 1998).
3
Micro Hybrid Option

• Advantages
• Provide a great deal of flexibility with I/O
  options (Discrete Analog) and now can even
  exhibit functions such as PID control.
• Great for controlling individual machines and can
  be networked today for increased communication.
• Per unit costs are far less expensive.
• 32 of PLCs utilized in industry belong to the
  micro classification.
• Relay Ladder Logic/Predominant Language used
  (Johnson, 2002).

4
Snazzy Graphs from Control Engineering Surveys
5
Micro Hybrid Option

• Disadvantages
• PLCs are predominantly used for digital I/O
  applications.
• Hybrid Micro PLCs offer additional analog control
  including PID and motor control, but are limited
  in the number of I/O per unit. For continuous
  process-heavy applications, distributed control
  systems (DCSs) are usually implemented.
• Processor speeds (Smith, 2003)
• However optimized code will always trump poorly
  written code. Programming experience is a must to
  maximize the capability of a platform.

6
Analog I/O Applications

• Demands placed on manufacturing for information
  gathering and handling require sensors that can
  do more than simply report an on or off
  condition.
• Sometimes it isnt enough for the proximity or
  photoelectric switch to just detect presence. If
  a reliable analog output were available, it could
  supply distance information, too (Mintchell,
  2001).

7
Analog I/O Applications

• A good, but unfriendly, application for
  inductive proximity switches is in stamping
  presses and dies. A prox is a good go no go
  sensor for part detection. But what if there are
  problems other than just part present?
• Like having the correct part, or the part
  inserted only partially by the feeding process?
  The solution could be with a prox, but with an
  analog output would work better than a myriad of
  small standard switches (Mintchell, 2001).

8
Analog I/O Applications

• Others
• Servo drives Motion control
• 30-40 of packaging machines are sold with servo
  drives and motion control content (Bartos,
  2003).
• Air-flow rates, control chamber and exhaust
  oxygen rates, blower rates, etc.. in furnace
  applications.
• Thermocouples used in injection molding of
  plastic parts.
• Strain gages used for testing mechanical
  qualities of products.
• Optical sensors for opaque versus clear object
  detection (Martin, 1996).

9
Our Research.Dual IR for Object Detection

• Our goal was to interface analog sensors (IR)
  with a PLC.
• The knowledge would be utilized later to include
  autonomous modes to robots used in future
  competitions.
• Our particular model uses the IR sensors to
  center the soda can.

10
The Physical Interface of an Analog input to the
Micrologix 1200

• Our Sharp IR sensors (GP2D12) are 3-wire
  transmitters, which were connected accordingly to
  the Micrologix 1200 analog module.

11
Input Measurements

• Before trying to program and play, there are
  switches that have to be turned on/off according
  to what input is being used voltage or current.
• Default is current.

12
Programming Your RLL to Accept the Input

• Scaling setting a range that the PLC can
  understand
• Raw/Proportional Format
• Range 0-32,760
• Scaled-for-PID
• Range 0-16,380
• Range inputs
• 0 10 volts
• 4 24 mA

13
How we scaled our parameters?

• Max voltage for the GP2D12 IR sensors are 2.6
  volts
• Max voltage for analog module is 10 volts
  32,760 using scaling to raw/proportional format
• 8,400 to 32,760 is proportional to
• 2.6 volts to 10 volts

14
Programming Your RLL to Accept the Input

• First rung
• Scaling IR sensor connected to the 1 and 1-
  terminals
• Output is N70
• Scaled min. and max. is percentage

15
Programming Your RLL to Accept the Input

• Second rung
• Scaling IR sensor connected to terminal 0 and 0-
• Output is N71

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Programming Your RLL to Accept the Input

• Notice that we want for both sensors to be
  greater than 67 (Source B)
• When this happens an output bit is activated.
• 67 is relative to the scaled min. and max. so we
  want above 67.

17
Programming Your RLL to Accept the Input

• When both bits are activated (both IR sensors are
  higher than 67), then we are looking for them to
  become equal.
• When they are equal and both higher than 67 we
  latch an output.
• Input 5 unlatches the output, so the process can
  be repeated.

18
Sources Cited

• Bartos, F. J. (2003). Automating your packaging
  lines. Control Engineering. Accessed online
  (August, 2003) http//www.manufacturing.net/ctl/i
  ndex.asp?layoutarticlearticleIdCA307746textau
  tomatingyourpackaginglines
• Johnson, D. (2002). Nano devices lead assault on
  traditional PLC applications. Control
  Engineering. Accessed online (August, 2003)
  http//www.manufacturing.net/ctl/index.asp?layout
  articlearticleidca236778
• Martin, V. D. (1996). Programmable logic
  controllers. Electronics Now, 67(4).
• Merritt, R. (2000). Hybrid systems take control.
  Control Magazine. Accessed online (August, 2003)
  http//www.controlmagazine.com/Web_First/ct.nsf/Co
  ntentframeset?openformMainSrcsearch
• Mintchell, G. A. (2001). Use sensors
  intelligently. Control Engineering. Accessed
  online (August, 2003) http//www.manufacturing.ne
  t/ctl/index.asp?layoutarticlearticleIdCA169118
  textusesensorsintelligently
• Reader Survey Programmable controllers (2001).
  What users want, now and in the future. Control
  Engineering Europe. Accessed online (August,
  2003) http//www.manufacturing.net/ctl/index.asp?
  layoutarticlearticleIdCA186196text22whatuse
  rswant22
• Smith, J. (2003). PLCs vs. PCs for industrial
  control. Plant Engineering, 57(6).
• Staff (1998). PLCs arent just older, theyre
  better. Control Engineering. Accessed online
  (August, 2003) http//www.manufacturing.net/ctl/i
  ndex.asp?layoutarticlearticleIdCA188788textan
  alogplc

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Demonstration