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View Full Version : Unsolved Using Stamps as cost effective industrial sensors and ctrls and integrating to SCADA?



rodrigjp
01-22-2012, 03:05 PM
Hi Everyone,

I am a newcomer to the microchip processing and programming arena and need some advice. I presently contract for a mining entity that are using Allen-Bradley and Rockwell SCADA systems to monitor the plant (crushers, conveyor belts, mills, liquid tanks etc..). The client is not happy with the cost effectiveness of the solution - mostly due to the exhorbitant costs involved in comissioning new functionality and maintaining these systems.

I studied electronics many years ago and in my opinion, feel that some of the simpler machine monitoring functions can be performed by more cost effective solutions (Such as a parallax processor) assuming they can be protected from the environmentals (Which I think is possible). I'm talking about sensing the temp of ball bearing casings to identify heat increases and avoid bearing seizures or a weighing solution to raise an alarm when, for instance, a ball mill is being overloaded.

I am not sure about these microchips ability to integrate to the Allen Bradley and Rockwell system, is it possible. An example would be to have a temp probe on a load bearing that is connected to a parallax cpu and when the temp exceeds a certain value, the CPU would send a alarm to the Allen-Bradley/Rockwell system on the HMI screen for the Operations guy to kick off a problem ticket.

I would like to know more from someone who may have actually done this and appreciate some advice.

Mike Green
01-22-2012, 03:37 PM
Welcome ... Be patient ... several of the forum members work or do consulting in this area (control of large industrial machinery) and frequent the forums. The Stamps have been used for this sort of thing for years

rodrigjp
01-22-2012, 05:11 PM
Hi Mike,

Many thanks and looking forward to it !

kwinn
01-22-2012, 06:40 PM
@rodrigjp,

Welcome to the forums. Yes, it is possible in most cases to replace existing PLC's and I/O modules with a microcontroller based module. Protection from environmentals is usually not that difficult since the newer electronics generally require much less power. In many cases I have mounted the electronics in a diecast aluminum case (Hammond) with the higher power chips using the case for a heat sink. For even higher power circuits I have mounted the power transistors on opposing heat sinks and filled the area between them with potting compound.

I would definitely recommend using the propeller chip for this kind of work. I have yet to tackle a project that it could not handle. My work is mainly in the industrial automation, building automation, and instrumentation areas, although I have had some exposure to mines and foundries as a result of servicing spark and x-ray spectrometers. In most cases I have been building modules to replace failed obsolete ones, or one that is available but ridiculously over priced. In some cases it has been to interface incompatible equipment (ie Weigand card readers to an RS485 security system).

Your biggest problem will be figuring out the signalling and communications protocols being used in the older systems. There was quite a variety of “standards” (Heintz 57 and then some) in use, and even more weird and whacky proprietary ones. A scope, protocol analyzer, and logic analyzer are extremely useful for this.

stamptrol
01-22-2012, 09:28 PM
ridrigjp,

Welcome to the forums.

The Parallax products can definitely work alongside some of the expensive big names. I've used Stamps in scales, pulp mills, saw mills and quarries for a number of years. The usual interconnection is by discrete contact (easiest for the HMI guy to put an alarm on the HMI screen) or to use RS-232 serial or RS-485 back to the PLC or other computer. Putting a Stamp onto Data Highway is expensive as the software overhead is high for the Stamp.

I would envision the best way would be to have the Stamp-based stuff on its own little network with a single connection (serial) to the PLC. As per your example, have a bunch of bearing monitors feeding a single Stamp which talks to the PLC on a serial link.

Be forwarned, if the equipment needs any agency approval ( UL, CSA, OHSA or some other authority) it can make the Stamp solution cost rise dramatically.

Keep the questions coming.

Cheers,

rodrigjp
01-23-2012, 07:00 AM
I'm definitely at the right forum !

Thanks Kwinn! Expense is definitely an issue as the function to price ratio is absurd - e.g. bearing temp alarm system probably > 15kUSD.

Hi Stamptrol, glad to hear I am on the right track. From what you said, I then take it that I can take a twisted pair discrete (on/off) signal direct to HMI computer and incorporate into Rockwell/Allen Bradley HMI software ?

Same question re RS-xxxx connect to PLC, would I be able to link straight onto Allen Bradley/ Rockwell system interface? Will it be easy for me to configure the software to read this input and display on the HMI screen or can only Rockwell engineers do this ?

Not sure what "Data HIghway" is but sounds like it may be an option - can you please send me a link to this product if you have ?

Given your information, I am going to invest in buying a propeller and a heat and pressure sensors, learn how to programme the prop to read these sensors and then attempt to link up to the plants PLC/HMI system using RS-x or TCP/IP and incorporate the Prop into the existing process control. Easier said than done, any advice would be greatly welcomed !



Once again many thanks for your valuable information, I sense this will be a long journey for me but the benefit to client may be attractive. Pardon my ignorance on the technical info. its been years!

rodrigjp
01-23-2012, 04:00 PM
Ok, so took a walk to my local electronics store and bought an entry level PLC based on PIC16f84a and an anlogue temp sensor to get me started. Also met a guy who says a TCPIP interfaceable PIC exists and can be connected to PLC/ SCADA networks ! So far so good, thanks once again !

Mickster
01-23-2012, 05:12 PM
Not sure what "Data HIghway" is but sounds like it may be an option - can you please send me a link to this product if you have ?



http://www.ab.com/en/epub/catalogs/12762/2181376/214372/1491278/3404058/index.html

N (http://www.ab.com/en/epub/catalogs/12762/2181376/214372/1491278/3404058/index.html)ot sure about your experience but AB used to send a posse of "engineers" out when we couldn't make their stuff work and all they did was RTFM for the first time ever, themselves...LOL!!!

Mickster

stamptrol
01-23-2012, 05:30 PM
rodrigjp,

Depending on the system, the HMI might be AB or a third party. Many of the large systems I worked on used one vendor for the operator interface in the control room and AB PLC's to accept the discrete inputs and output the discrete outputs.

Data Highway is AB's proprietary communication protocol among the AB hardware. But, it is also possible to have an ordinary serial port available as well.

Start small and work into it! I'd suggest getting your feet wet by successfully getting your new micro to read one or more temperatures and perhaps have it drive a relay when it goes into alarm. Then, set aside some time to get the alarm status back to the PLC/HMI. The communications, if you go that way, will be the most challenging.

Cheers,

kwinn
01-24-2012, 03:27 AM
@rodrigjp,

The hardware end of things is pretty simple. The difficult part is the communications protocol. The data highway uses RS485 at the hardware level so no problem there. With the addition of an RS485 driver chip and an adc a propeller chip could measure and send data from 8 sensors.

Mickster's link provides a general overview of the system, but there is a lot of detail left to discover. My approach to this type of project has been to find the points where the data input and data outputs are the simplest (usually the analog input signal and the serial/parallel data output) and replace everything in between. Not always easy or practical to do.

Temperature sensors are typically one of the following:

Thermocouple: capable of measuring very high temperatures. Usually needs an amplifier (op amp) and an ADC.

Thermistor: medium temperature range. Needs a series resistor and an ADC.

Both of these are non linear so require some processing to get temperature.

Solid state sensor:

Produces an output voltage proportional to the temperature. An op amp and ADC can produce a digital temperature reading.
There are also solid state sensors that output temperature as a pulse width signal or as a serial data stream. These can be converted directly and transmitted to an RS485 bus by a propeller.

Force Sensors:

Force sensors are typically strain gages or load cells that are made up of strain sensors in a wheatstone bridge circuit. They usually require a drive signal, and the analog output signals are typically low and require amplification and an ADC.

Speed/Direction sensors:

These are typically optical or magnetic with pulse output or quadrature encoders. These can be converted directly and transmitted to an RS485 bus by a propeller. In some cases speed and direction sensors will output a voltage proportional to the speed and direction, or output a voltage proportional to the speed and a separate signal (high/low) for direction. An ADC would be required for the analog speed signal.