I have incoming 8 type T thermocouples (they share a common constantan leg) and I wish to filter EMI noise coming from a nearby large variable-frequency drive. Omega sells TC connectors for this purpose with built in ferrite cores (90 ohm @100Mhz), they also sell some separate cores (155 ohm @100Mhz). Google-ing turned up a couple of users who run the TC through a figure 8 dual-hole core, presumably for better "matching". I'm guessing they ran one lead through one hole (simply pass it through, not multiple windings) and the second through the other hole...does this sound correct?
What technique is better? (1) run each leg through a separate core. (2) Run both leads through one core. (3) Use a 2-hole core. Since all the TCs share a common "leg" options #2 and #3 are possible but will not be too pretty (the common leg will have 8 ferrites on it).
Other questions on ferrites: Is bigger (ohms) better? Note that the measured tempearture is relatively constant (changes 5F in one minute). Should the core be relativley snug around the wire(s)?
Thanks in advance jj