Cliff
Thanks for the detailed explanation. I'm sure others will find
it helpful too.
Best Regards,
Doug J
In a message dated 4/2/2005 11:34:19 AM Central Standard Time,
dr_redus@devtex.net writes:
Doug,
My background is in mechanical engineering. This was my first hands
on project with a PLC. I found working with the PLC to
be straight forward. The documentation that comes with the
Automation Direct is detailed and very usable with lots of examples.
Also the tech support from Automation Direct was great. I think this is
generally true for all the PLC suppliers. Anyone that has done any
programming in C, VB or even FORTRAN (I'm dating my self) would have no
problem picking up PLC ladder logic. My starting point was to make a list
of the what I/O I wanted in my boat such as, for example, an analog input
would be a pressure transmitter for ambient water pressure or tank
pressure. A digital input channel would be something like the hatch
switch or a limit switch or a button on a joystick. An Analog output
would be like a PWM signal to a proportional pressure regulator and
digital output would be, as an example, a coil on a solenoid valve
for air to blow the main ballast tank. After you know how many input and
output channels you will need, then you can look at the PLC modules and decide
how many you need of each. This will set the number of slots you will
need in the PLC base. My suggestion would be to have a least one open slot for
future changes. After plugging in the modules, it is a matter of
programming each module. My learning curve was greatly helped by a
fellow PSUBer, Alec Smyth, who sent me a copy of his ladder logic. By
studying what Alec had done and reading the documentation from the PLC vendor,
I was able to come up to speed without to much grief. I did find the
instruction set available on PLC's to be primitive relative to higher level
languages such as C or VB. Most sensor manufacturers offer either 0-5VDC
output or 4-20mA outputs. After discussions with an engineer that does a
lot of mobile automation work, I choose to go with 0-5VDC for my
sensors. Anyone with basic skills in electronics ( can use a multimeter
and can solder) can pick this up. As to PC104 experience, I
have none. One suggestion I would make is to stick with one PLC vendor
for all the modules and the touch screen display. This makes trouble
shooting a lot easier. One other point, if you have any sensors that
require RS232 communication in ASCII, you have make sure the CPU module you
pick support receiving ASCII as some do and some do not. One of the good
suggestions I received from a fellow psuber that had fabricated a psub was to
wire up all the instrumentations and equipment on the bench in approximately
the correct location prior to installing in the boat. This
proved to be very helpful in debugging everything and in making up
the wiring harness with disconnects. Part of my interest in building a
psub was to come up to speed on PLCs and instrumentation. This part of
my fabrication has been a lot of fun. I did not buy any specific books on
instrumentation. I did do a Google search on basic instrumentation
wiring and found quite a bit of guidance. The real work in using a PLC
as the onboard computer has nothing to do with the PLC, it is having a good
plan of how each ship system is going to operate and interface with the
overall design.
Cliff
----- Original Message -----
Sent: Saturday, April 02, 2005 9:03
AM
Subject: Re: [PSUBS-MAILIST] computers
in subs
Cliff
Yup, that is out of my budget. But I have a friend, and fellow sub
builder that wants to go all out on his control and monitoring system
including the touch screen. So what is the leaning curve for PLC and
the required electronics of sensor integration? And what web, book,
and or training resources would you recommend for someone with beginner
digital electronics abilities and good object and structure programming
skills, but no PLC?
Is automation control your field of work, or did you develop this skill
for your sub? And so do you have experience with PC104 ( www.pc104.org)
and would that be a better approach for someone with C or VB experience but
no PLC?
Thanks again
Doug
In a message dated 4/2/2005 8:38:24 AM Central Standard Time,
dr_redus@devtex.net writes:
Doug,
The cost breakdown for the Automation Direct PLC system on my boat
is: PLC hardware $2183, Software $394, color touchscreen display $745 and
joystick $469 for a total of $3791. If you are patient and know what you
want, you can pick up I/O modules on Ebay at a significant discount.
As an example, an Ebay search string Automation Direct will usually turn
up a list of available PLC modules.
Cliff
----- Original Message -----
Sent: Saturday, April 02, 2005
12:41 AM
Subject: Re: [PSUBS-MAILIST]
computers in subs
Simon,
I know it's out of my league, but out of curiosity, what is the
price tag for that setup?
Thanks --Doug J
Simon,
For the 1 atm sub I have under
fabrication, I am using an Automationdirect (http://web4.automationdirect.com/adc/Home/Home),
DirectLogic 205 series PLC (Programmable Logic Controller) with a
6" color touch screen display which is used to interface
with the controller and for all gage displays. The PLC base has
9 modules, 1 CPU, 3 analog input, 1 digital input, 1 RTD input, 1
analog output and two relay output modules. The PLC is currently
configured with 20 analog input channels, 12 digital input channels, 4
RTD temperatures inputs, 4 analog output channels, and 18 relay output
channels. The CPU module (DL 260), which is about the size
of a bar of soap, has two RS232 ports, one of which is used to connect
to my compass/roll/pitch sensor and the other is connected to the
touch screen display. A dual axis joy stick is used for roll
and pitch analog input to the PLC and a potentiometer on the
rudder pedals is used as an analog input for yaw control.
The joystick has 6 switches that I use for blowing and flooding
the MBT and VBT as well as moving the trim weight forward or aft via
a power screw driven by a hydraulic motor. This
setup gives me fly by wire capability. A laptop PC was
used to write the ladder logic, design the screens and download the
ladder logic and screens into the PLC. All is working fine on the
bench and I found the system to be quite flexible in changing inputs
and outputs to the PLC and modifying display screens.
A PLC was chosen over a hardened PC for
robustness and to minimize space. The PLC is powered from either the
main battery bank (120 VDC) via a DC-DC converter (120 VDC to 24
VDC) or from an independent emergency battery pack (24
VDC).
Cliff
----- Original Message -----
Sent: Friday, April 01, 2005
5:08 AM
Subject: [PSUBS-MAILIST]
computers in subs
NEW
TOPIC!!
Who uses onboard computers on their subs? Are you
using modified
trimix SCUBA computers, or homebrew type
stuff?
Simon,
You mean a dive computer or a normal? On a 1
atm sub a deco computer makes no sense.
If my sub is operational again; I consider a
pocket pc for instument reading ,listing checklists, gps navigation
and as video camera display/capture.
There are probably more possebilities and it
might save space.
disadvantage: not water resistant
regards Emile
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