Every Device on the low-speed CAN network requires termination resistor for each CAN data line: Rth for CAN_H and Rtl for CAN_L.The tranceiver on the NI CAN cards is a Philips tranceiver and Phillips recommends an overall Rth andRtl termination of 100 to 500 ohm ( each) for a properly terminated low-speed network and an individual device Rth and Rtl termination of 500 ohms to 16Kohms.The PCI CAN /LS board ships with the 510 ohm resistors, but also includes 15k resistors in the kit.
Please refer to the "Getting Started with the NI CAN hardware" manual , Appendix D ( Cabling Requirements for Low Speed CAN) on a detailed description on determing which resistor value is more appropriate for your low speed application.
The link to the manual is given below:
http://search.ni.
com/search/query.html?col=alldocs&qp=%2Bcontenttype%3Aproductmanual&lk=2&layout=ProductManual&qt=CAN