O2 sensor placement and tips, from Those in the know.

I had these sent to me in a technology for tuners newsletter from Innovate, the people who make wide-band sensors and data collection systems:

Not getting the life out of your O2 sensor that you expected? Follow these steps to insure award-winning accuracy and maximum sensor life:

Sensor Placement. The sensor bung (or boss) should be at least 8" away from the combustion cylinder (at or after the collector if you have one, unless you're installing a sensor for each cylinder). To avoid condensation running into the sensor, it should be installed at the side or on top, NOT on the bottom of the exhaust pipe, for example between the 10:00 and 2:00 position. If you don't have a bung, any muffler shop can weld one in for you. If you have a catalytic converter, install the sensor before it. If you have a turbo, install the sensor AFTER it.
Temperature. Temperature at the bung should not exceed 500 degrees C or 900 degrees F. (Extended bungs help with hot locations, see next item).
Extended bungs. For high performance and power sports applications, we strongly recommend using 1" bungs (p/n 3764.) These longer bungs increase sensor life in the "richer" conditions encountered under boost, leaded fuel use, or two-stroke applications.
Safety. Sensors get very hot. Usually this is a non-issue, since they are safely in the exhaust bung when in use. However, if you have the sensor out (for example during a free-air calibration), be sure not to touch the sensor tip, or let it touch a combustible surface.
Never leave an unconnected sensor in running exhaust. An un-powered sensor will be damaged when exposed to exhaust gas.
Sensor Life. Wideband oxygen sensors are designed to withstand the harsh environment of combustion exhaust for 30,000+ miles. However they are complex electro-chemical devices, and lifespan can be reduced by: A) Running leaded gas; B) Running very rich (less than 12.5 AFR) for long periods of time; C) Hitting a heated sensor with water droplets; D) Hitting a running sensor with silicon spray (like WD-40, etc.); E) Dropping a sensor on concrete.
Sensor Errors. Your Innovate wideband will communicate an error code when it detects sensor damage (unlike analog widebands that will give you slow or false data). Depending on your gauge, the error state may be a full-lean reading, an "E08" (or other "E0x"), or a blinking LED. When you see an error condition, first do a sensor calibration, and, if that doesn't solve the problem, replace the sensor. (For races and remote rides, carry a spare).
Calibration. Direct DigitalTM allows you to calibrate the sensor to compensate for sensor wear and changes in barometric pressure, etc. YOU MUST CALIBRATE EVERY NEW SENSOR before first use. The calibration procedure requires that the sensor be in free air, so first remove the sensor and disconnect from the LC-1. Next, to clear all stored calibration data, power the LC-1 for 10 seconds without the sensor attached. Finally, attach the sensor securely and power up again in FREE AIR (no exhaust whatsoever) for 1 minute, or until your gauge warm up indicator stops (full rich or "Hxx"). Unless you see errors, calibration is only required every 15,000 miles. (For turbo and blown applications, calibrate every 10,000 miles. For race applications, calibrate once per race weekend. For Dyno applications, calibrate weekly, depending on use.)