>I'm working on a data logger which is a little different than what I've >done before. > >Now my question: > >How do I hook these separate analog signals up without sharing the ground >with the Power circuit? > It sounds as if your customer has SOME budget for moderately expensive parts. I'd use a 2 port or 3 port isolation amplifier. I've used both the Burr-Brown 3656 and the Analog Devices AD210 - I prefer the AD part. They cost about $50 USD and are worth every penny in situations such as yours. They require a single 15 Vdc power source - this source can be isolated from both the input and output. The input looks like a standard op-amp - you treat it as such when setting gain, etc. The output is a unity gain op-amp. There is auxiliary power available at both the input and output side of the module. The AD part is good for 10 or 12 bits of accuracy (I don't remember the exact linearity spec). PS - the difference between a 2 port and 3 port amplifier: the 2 port generally shares a common ground between the output and power supply; the 3 port is completely isolated between input, output and power supply. The AD210 is spec'd at 2500 VAC between input and both other ports; 1000 VAC between power and output. They are tested and must pass at MUCH higher voltages than those. There are other ways around your problem, but the easy ones (much harder than the isolation amplifier) don't have much accuracy. Hope this helps. dwayne Dwayne Reid Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax Celebrating 15 years of Engineering Innovation (1984 - 1999) * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * Do NOT send unsolicited commercial email to this email address. My posting messages to Usenet neither grants consent to receive unsolicited commercial email nor is intended to solicit commercial email.