Mini PLC with networking

[Oceansoul]

I have been tasked with a job to count the number of people in a site basement and display this information to the sites control room. Currently there is no system in place and the control staff do not know exact numbers of people in the basement.

The basement is a large area, but is not a confined or 'zoned' space. There are 9 or 10 (awaiting confirmation) staircase entrances to this basement. My plan is to have a mini PLC at each entrance with 2 push button inputs (one for person going in, one for person coming out) and enough outputs to drive 2 seven segment displays. These PLC's will need to be able to communicate with each other. Can anyone recommend such a PLC? We would usually use AB Rockwell PLC's but for this project I am able to use whatever suits. Preferably not using Ethernet, as I would then have to apply for IP address and the systems team would probably request AB then.

 

[adisharr]

I have been tasked with a job to count the number of people in a site basement and display this information to the sites control room. Currently there is no system in place and the control staff do not know exact numbers of people in the basement.

The basement is a large area, but is not a confined or 'zoned' space. There are 9 or 10 (awaiting confirmation) staircase entrances to this basement. My plan is to have a mini PLC at each entrance with 2 push button inputs (one for person going in, one for person coming out) and enough outputs to drive 2 seven segment displays. These PLC's will need to be able to communicate with each other. Can anyone recommend such a PLC? We would usually use AB Rockwell PLC's but for this project I am able to use whatever suits. Preferably not using Ethernet, as I would then have to apply for IP address and the systems team would probably request AB then.

If you have limited I/O needs, why bother networking a bunch of controllers and just run the I/O to one controller. 24VDC I/O can go a long way.

 

[the_msp]

I would use break beam sensors instead of push buttons. What if people forget to log in and out? You will still need two sensors at each location, a and b. By looking at the rising/falling edge triggers, you can determine if the person is coming or going.

Regarding the IP, you do not need all the controllers given an assigned IP by the company. You can use your own range (e.g. 10.xx.xx.xx) and have them talk to each other on this.

 

[Oceansoul]

I hadn't thought of using beam sensors. I think this is a better way to go. Also the more i think about it for the cost of 10 small PLC's i could probably just use a micrologix in a central location. The wiring is not all that far really. <100m from the centre of the building to the furthest entry points, so 24VDC I/O will be fine.

 

[jraef]

I worked for a security access company for a while, we used a "gate" approach with through beam sensors in series to detect the direction of movement (in or out). But it might not be as simple as you think. How will you prevent the system from being "fooled" by people passing by at the exact same time in opposite directions, walking side-by-side, dragging wheeled luggage, running, or stopping IN an access point while others pass by? It gets messy really fast if you can't funnel people through a narrow gate, like a train or amusement park turnstile. But from my experience, basements are often tricky because you have issues with not impeding flow of traffic in or out during an emergency, and/or handicapped accessibility, which precludes restrictive barriers in many jurisdictions. It's hard to beat a camera and a human brain to assess the situation, which is how most basement applications ended up for us.

 

[Stephen Luft]

Based on the information you have provided, something like the FMD1616-10 should work for you. Should you only require 8 outputs, then the FMD88-10 would suffice.

It has 16 outputs, RS485 and ModBus RTU protocol for connecting controllers. RS485 can communicate upto 4000 feet.

http://www.eternity-sales.com/tri-plc/fmdseries.htm

Do you want to display counts at each location or will there be a central location?

Disclosure - ESI is an authorized TriPLC distributor.

 

[tragically1969]

I have been tasked with a job to count the number of people in a site basement and display this information to the sites control room. Currently there is no system in place and the control staff do not know exact numbers of people in the basement.

The basement is a large area, but is not a confined or 'zoned' space. There are 9 or 10 (awaiting confirmation) staircase entrances to this basement. My plan is to have a mini PLC at each entrance with 2 push button inputs (one for person going in, one for person coming out) and enough outputs to drive 2 seven segment displays. These PLC's will need to be able to communicate with each other. Can anyone recommend such a PLC? We would usually use AB Rockwell PLC's but for this project I am able to use whatever suits. Preferably not using Ethernet, as I would then have to apply for IP address and the systems team would probably request AB then.

Why reinvent the wheel Just buy an off the shelf access control system ?

 

[MartB]

Is this supposed to be an access control system or a rough 'guesstimate' of the number of people in the basement?
In other words, how accurate do you require this system to be? How important is that number of people in the basement?
Do people already carry some form of access control for other parts of the building? (i.e. RFID tags, swipe cards)

All of these are important questions that need to be addressed before worrying about which form of control to use.

 

[Firejo]

You could use a MicroLogix 1100 with one of these systems (see link below). The PLC would talk to the PLR6435 (protocol master) via either DF1 or Ethernet/IP and would read the inputs and control the outputs of up to 16 remotes. You would have a PLR6430 remote (I/O remote) at each stairwell giving you up to 8 discrete inputs at each location and 8 discrete outputs (enough for a 7 segment display). It’s not cheap but it would do the job.
http://www.data-linc.com/cixfamily/cix6400.htm