> From: Scott Dattalo <sdattalo@UNIX.SRI.COM>
>[cut]
> Why do you use the relays? Do you need the low on resistance they
> provide? Do you need the the galvanic contact-to-coil isolation?
>
> If it's an isolation issue, have you considered solid state
> relays? These are available with on resistances <20 ohms (which
> is extremely large compared to a relay), isolation barriers
> as large as 3kv, and contact ratings as high as 400V (if not
> higher now).

Uh, I think the guy wanted low level analogue control, not
phase control of his electric furnace.  (Steve waxing sarcastic
here...)

I think for the ultimate in low noise application he is correct
in selecting relays (so long as he doesn't want to switch too
rapidly).  The mercury-wetted contact has much lower noise than
a FET (its 'RDSon' is heaps lower) and there is less capacitive
coupling from the control - FET gate capacitance is at least
a few pf.

Regards,
SJH
Canberra, Australia