I use the DS1620 over several (~10) metres. I found I had to terminate the data and clock lines with a 120 ohm resistor and a 0.1 uF capacitor to ground to prevent ringing on these lines which screwed up the data stream. I also put a 10 uF across the DS1620 power to ground pins.

I realise the DS1820 is not the same as the DS1620 but the ringing issue may be the same.

HTH
BrianT