Conversion: Mechanical to Digital Input

henno2000

Member
Join Date
Jan 2007
Location
UK
Posts
72
Hi,

I have been asked to convert part of an existing system which uses mechanical inputs in the form of switches from a remote location. This remote location is to be converted to a PLC (Siemens S7), but for the time being keep the original infrastructure of the main panel.

Looking at the problem, the mechanical inputs to the system would now become digital outputs of the PLC back to the original board.

There is a common control voltage and the rest of the contacts are either NO or NC.

Because of the fact that the digital output card of the PLC supplies a voltage, is there any simple way to convert these to volt free outputs? (Or alternatively, retain the state of these controls as input?)

Regards,
henno2000
 
I can see why you seem to be confused. You have totally confused me in less than 10 seconds.

You need to back up about 10 steps.
1. State what the machine process is
2. What these mechanical input thingys are
3. What you want to control in the process

Dan Bentler
 
leitmotif said:
I can see why you seem to be confused. You have totally confused me in less than 10 seconds.

You need to back up about 10 steps.
1. State what the machine process is
2. What these mechanical input thingys are
3. What you want to control in the process

Dan Bentler

OK,

  1. The function of the system is to control lighting for the navigation of ships. There are four possible combinations in which to control these lights. These controls can either be operated from the local panel, or a remote panel in the operator cabin. (The remote one is to be replaced by a PLC). The original panel is to be left unchanged for the immediate future.
  2. The mechanical inputs are the inputs to the system in the form of selector switches to provide the four different combinations of lighting sequences.
  3. For the process, I am wanting to simulate the existing remote station via a PLC/SCADA system instead of using physical inputs. Therefore, the original inputs will now be digital outputs of the PLC. The inputs shall be provide in the form of buttons on the SCADA.
Hope this is clearer.

Regards,
henno2000
 
So what HMI will you be using?

This should not be hard. You will have bits that you will set in the HMI. In the plc program you will map these bits and put them with the inputs.

for example if you input is I100.0 then M100.0 is programmed in the HMI and included in the PLC program.
 
CharlesM said:
So what HMI will you be using?

This should not be hard. You will have bits that you will set in the HMI. In the plc program you will map these bits and put them with the inputs.

for example if you input is I100.0 then M100.0 is programmed in the HMI and included in the PLC program.

SIMATIC WinCC is the SCADA package.

With the old system, the selector switches were originally an input from the old system. (Via NO or NC contacts). Now these inputs to the old system will be coming from the output of the PLC, which shall output a voltage (instead of just closing or opening a switch).

The inputs to the PLC will be the outputs from the original system indicating the status of device.

What I am asking is if there is a suitable method to apply a NO/NC state from a digital output without applying a voltage from the PLC. (IE - Would additional relays have to be used, or is there a more efficient method?)

Regards,
henno2000
 
henno2000 said:
What I am asking is if there is a suitable method to apply a NO/NC state from a digital output without applying a voltage from the PLC. (IE - Would additional relays have to be used, or is there a more efficient method?)

It seems to me that this will be dependant on the _exact_ requirements of the legacy system. I'm not familiar with S7, but most PLCs will offer relay output modules. These would look like a dry contact to the outside world. Note that most PLCs will have one leg of a group of outputs tied together for logistics sake.

Whether using relay output modules tied directly to your legacy system will be simpler/more efficient/cheaper than having relays is something you will have to work out using an electrical diagram of the old system. Depending on the loads involved, it maybe desireable, or even necessary, to have additional relays.

Brian
 
Yes, looks like I shall have to use a 24VDC relay to close the various contacts, just wondered if there was a more efficient method of doing this.

Thanks
 
What about remote IO like ET200 ? Maybe this could carry the switch positions from the remote locate to the main PLC
 
Henno2000,

To replace the remote buttons with a PLC (controlled with SCADA inputs), buy a Simens PLC with some Output modules that have relays built-in (commonly called PLC Relay Output Modules, where the PLC controls the relays in the modules directly).

Using Relay Output Modules, your controls on the other end can be practicaly any voltage, although you do have to consider how to make one side of the circuit "common" as Brian mentioned, so that you can use the PLC Relay modules (which have one side of the relay contacts tied to a common wire).
 

Similar Topics

I have a Type C to RS485 adapter connect to my Siemens RWF55. I use modscan to scan it to get a value from the Siemens controller. In the...
Replies
4
Views
75
Hi all, I'm in the process of upgrading a PanelView1200 HMI program to be developed in FactroyTalk View Studio. The filetype for PanelView 1200...
Replies
7
Views
245
Hi All , I am working for a project to convert S5 PLC to S7 PLC system for a Concrete Block making machine of OMAG . I request guidence and...
Replies
11
Views
543
Hello, I have converted RSView 32 to FTView SE 14 (I have tested FTView 12 before as well and there were some difficulties so I moved on to...
Replies
4
Views
185
Hi, Im doing a project with a Power meter that offers Modbus TCP and each signal is a 32bit Float.¨ I tested the float in Modbus Poll and...
Replies
22
Views
2,961
Back
Top Bottom