Multiable RS-232 Devices

[Mike_PAC]

 I am starting a project that I will extract data from four (4) Laser sensors. Only communication available is via RS-232. The laser sensors will sent a data value out representing a distance
( 0 -12" ) that is measured. The data from each of the sensors will only be sent when a photo-eye detects the presence of the object. Conveyor speeds are SLOW!!! Object will be in the window for 3 - 4 secs.
 Will the T100M888+ be capable of this task? Only output is a digital one to light a indicator light to alert the operator that there is a problem.

[support]

Is the PLC able to control which laser sensor to activate so that the laser sensor will then start measurement and send data to the PLC? If so, then you may be able to multiplex the RS232 to the 4 laser sensor using relays. All you need is to multiplex the RS232 transmit signals from the laser sensors to that of the PLC's receive signal pin.

On the other hand, if more than one laser sensors could send out data to the PLC simultaneously, then you need 4 independent serial port so that no serial data will be lost. Since each T100MD888+ has only two serial port, you can only interface to two laser sensors (one convert using Auto485) per PLC, and you need two PLCs to interface to four sensors. The two PLCs can handshake with each other using digital I/O line to communicate the pass/fail status of the two sensors under their charge so that there is only one pass/fail indicator light to report a trouble.

[benb2000]

Why not convert all the RS-232 Laser interfaces to RS-485, and put them all on one multi-drop network?

[support]

That's certainly a possibility provided that the PLC is able to schedule for only one laser sensor to send out data at a time to the PLC. Each laser sensor will need one Auto485 to convert their RS232 to RS485 and multi-drop to the PLC. If the laser could send data anytime it wishes then this wouldn't work since more than one laser sensor may try to send data at the same time which will corrupt the data.

[cdenk]

a thought, take the RS-232's through 4 small relays, select the relay to be active with 4 of the PLC's outputs. probably could also be done with a multiplex sort of chip, or a chip with 4 "AND" gates, could be TTL if the RS-232 levels are 0 and 5 VDC (non-standard)