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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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