Problem Controlling Relays with Digital LinesHardware: Digital I/O (DIO)>>Static, Multifunction DAQ (MIO)
Problem: Why am I having a problem controlling relays using the digital lines from my DAQ board? Sometimes the relays work and sometimes they don't. Solution: If you are working with electromechanical relays, the DAQ board may not be able to supply enough current to operate the relays. This is a difficult issue to troubleshoot because it may supply enough current to drive one relay but not multiple relays. When trying to drive multiple relays with insufficient current, it may be a different relay or relays that work each time the program is run. A good way to check for this condition is to test the relays one-by-one. If the relays work individually, but not together, then this is probably a result of the board's output current limitation. If you are using a DaqCard in particular, be aware that the PCMCIA bus is capable of supplying only a small amount of current that is often not sufficient for driving relays. If possible, test the operation of the relay using an external power supply. Electromechanical relays do wear over time, so a bad relay module is still a possibility. See the link below for a Developer Zone document that describes common connections for Digital I/O. It addresses the issue of connecting relays to digital lines and contains diagrams showing how to do this. Related Links: Developer Zone: Common Hardware Connections for Digital I/O and Counter/Timer Boards Attachments:
Report Date: 10/06/2004 Last Updated: 07/19/2007 Document ID: 3E5JKPAU |
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