Which PLC should I choose ?? (Idec RAM problem, part II)

Dear all

I am making a datalogger which is logging visits to a public toilet. I am currently using an Idec MicroSmart 20RS1, equipped with 64kb and a clock module.
This is my first PLC experience and in my naive PC way of thinking, I thought that I could use all these 64000 bytes for storing my data.
As I am now aware of, this is not the case. I have only access to 7300 data registers, which means that I can only log around 7200 visits. And that is far from enough !

Is there another PLC brand which allows me to use all of the memory for data ? (and even have more memory ?? )
It should prefereably be around the same price and physical size as the Idec MicroSmart.

Best regards
Jorgen Brix

Qbrix,

We need more details, please! How many items of data are you collecting, and how many bits in each item? I would think that visits to a publilc toliet could be adequately logged just by counting each person that enters. Any off-the-shelf PLC can count to 32,000 with each counter, and by cascading several counters, you can count to millions. Apparently there is more to this than I can imagine.

Check out Entertron for a datalogger.

http://entertron.com/


regards.....casey

Hi again

And hi Lancie1. Yes, there is more to it. I need to log an approximate timestamp for each visit and not just a counter. Therefore I need 2 bytes for each visit which reduces the number to around 7200 visits. I'm also programming a HP iPaq with a serial cable to fetch the data from time to time. And as "time to time" can be with months inbetween, I certainly need more than 7200 logs as some toilet are used quite frequently.

I stmubled across this one last night: The Allen-Bradley CompactLogix

It might do the trick although I have no clue about the price.

Best regards and thank you for your replies
Jorgen Brix

Qbrix said:

I need to log an approximate timestamp for each visit ...

Click to expand...

Why ? If I had a computer this would be the easy way to do it and let who ever got the data to do what they want with it.

What form are they going to reduce the data to ? Knowing that, you can store way more visit data than using a 16 bit timestamp for every visit.

For instance:

1. Use each register for number of visits in every 20 minutes interval. That gives 3 months of data for about 7000 registers. Not expecting more than 255 visits in 20 minutes ? Then use only 2x8 bits of the 16 bit register for each interval for 6 months, or make the interval half (10 minutes) for the same 3 months of data.

2. Time the interval between visits and put that in each 8 bit register. Or use 4 visit intervals of 4 bits each:

#0 = 0 - 1 minute interval between last and this visit.
#1 = 1 - 2 minute interval
#2 = 3 - 6 minute interval
#3 = 7 - 12 minute interval
...
#14 = 60 min to 120 minutes.

Use a marker of 0xFFFF (all ones) to mark a new day.

3. Use only 8 bits for the time stamp. That gives you 6 minute accuracy. Then use #255 to indicate a day change just in case no one visits for over a day. Record the start time ( of all data collection - when the table is empty) in a set of registers and then each new visit register (8 bits) is an offset from it in each day.


Run the above by your client and see if any meet what they are going to do with the data.

I have only access to 7300 data registers, which means that I can only log around 7200 visits. And that is far from enough !

Click to expand...

So, how many is the minimum/maximum ? And what is the maximum time in months that you will allow data to be stored ? Both need to be defined. Either you tell your client and they agree or they tell you and you find a plc / data logger that can handle it.

Dave

How embarrasing..

Hi Dave

I can only say Thank you (!), and that it is very embarrasing, that I didn't see that solution before.

I'm not quite sure why I was so stuck on my initial solution. Being a professional PC programmer through many years, I should have done better.

I am now sticking with the Idec MicroSmart and count number of visitors for each 15 minutes. That gives me a 5 month interval between the data needs to be fetched. That should be more than enough.

Thank you very much again.

Sincerly
Jorgen Brix

I went back to look at Entertron's "logger" and it appears to plug into any serial plc.

Overall, it appears very interesting, and lots of GOOD tech support for FREE!

Unit will store 16,380 records.

DATA can be downloaded as an excell spreadsheet.

Logger "LINK"

Logger manual "LINK"

regards.....casey

Qbrix said:

Is there another PLC brand which allows me to use all of the memory for data ? (and even have more memory ?? )
It should prefereably be around the same price and physical size as the Idec MicroSmart.

Click to expand...

Hi Jorgen

Regarding price, size and memory, I would suggest the Swiss PLC brand SAIA PCD.

For instance the PCD3 series: http://www.sbc-support.ch/pcd3/mxxxx/Ex_Beilageblatt_PCD3.Mxxx0.pdf


Smallest is the PCD3.M3020 (price in Norway: 4981,- NOK)

It has:

16384 x 32 bits registers (Dword)
Memory: 128 Kbytes RAM (Divisible by User program/Webserver/Data Block)
Realtime Clock
USB interface
etc

A Data Block is an "array" of 32 bits elements. The amount of free memory decides how many DB's you can declare.

NB: You have to use I/O slot #0 for a batterymodule, since 8 h data protection with a cap is to risky...


If you need more memory, there are larger CPUs


Regards

Karl