Basically there are three choices. OPC,
ABRSLINX or a Citect driver (e.g. ABTCP5)
In general, I believe that the Citect drivers are the best
option, (when they are an option), for the following reasons.
The Citect I/O Server communicates directly with the field
device (OPC and ABRSLINX go via RSLinx). Thus there is no added
delay from 3rd party software.
If a problem is found with the driver than it is easier to
rectify when 3rd party software is not involved.
Following are some example situations.
- If the PLC is a Controllogix processor than use the OPC
driver.
- If your PC has a KTX card, or a card of the like, than the
Citect driver will require the WinRT service on start-up. RSLinx
does not use WinRT and we thus we have a conflict. Citect cannot
start if RSLinx is running and RSLinx cannot start its native
driver if the WinRT service is running. I have a feeling that the
WinRT service can be stopped after Citect is running, but NT
security is generally set up to disable control panel access. If
you wish a Citect I/O Server to be a PLC code editing station then
the ABRSLINX driver is probably a better option. The best solution
is to have separate PCs for the Citect I/O Servers and PC
workstations, all with KTX cards and use a Citect driver
(ABTCP5).
- If you communicate with your PLC serially than I would use the
ABRSLINX driver. At present, Citect's serial (KE500) driver's
communication method with serial devices is half duplex using BCC
error checking. RSlinx's serial driver uses full duplex and CRC
error checking. What this translates to is that after you get the
device talking to Citect, the PLC software cannot communicate with
the PLC. If you wish to change the PLC code then you have to wipe
the PLC (i.e. power off and battery out) to restore factory
defaults, then download PLC code and then make changes. This is
probably OK in a batch type process or where code will not be
changed, but...I personally do not like it.
- If you connect directly to your PLC via Ethernet then I would
use a Citect driver. (NB. I am not talking about the Controllogix
Ethernet module)
- If you connect to your device via the Controllogix gateway
(e.g. via DHRIO module), then I would use the ABRSLINX driver.
- And finally, if Citect does not have a driver, or does not
support the connection method, for the device than I would use the
ABRSLINX driver.
All of the above are only suggestions and are not the only way
to do things. If your PLC network uses a variety of communication
methods than you it may be wiser to make a compromise for
conformity.
|