I have an Enwatch unit with a bias voltage of 4. We verified this with a volt meter. The data
looks fine. When we go out to the junction box between the accl and enwatch
we get a bias voltage of 12. We tested another board and got the same
results. Sounds screwy, huh. Not a PX. Any thoughts would be appreciated,
thanks.

Where did you measure 4 volts on the Enwatch?

Set up a bias voltage reading in Odyssey and see what you get from them.
I'm with vibbase, where were you measuring? Directly across the inputs on the bottom of the board? You sure you were on the right pins?
Remember, white is signal, black is common

Dave

The bias voltage of 12 volts at the accelerometer is right in the range that's expected. It can vary between 10 - 14 volts depending on the accelerometer.

With some type of accelerometers, the bias voltage can be a function of temperature or change in temperature. Is the accelerometer located somewhere where it could get very cold or go through large temperature swings?

Is there any chance you were meauring CURRENT at the Enwatch? Somewhere between 2 - 10 mA is the usual range for ICP-type supplies.

Here are some simple checks to make:

1. With the accelerometer disconnected, you should measure 18 - 20 volts across the input terminals (or at the accelerometer connector). If you meaure much less than this, verify that the instrument is on and set up correctly.

2. With the accelerometer disconnected, you should measure 2 - 10 mA across the input terminals (or at the accelerometer connector). If you meaure less than 2 mA, verify that the instrument is on and set up correctly.

NOTE: Because the ICP supply is a constant-current source, it's ok to measure current directly across the terminals. Do not do this with a regular power supply or a battery!

3. With the accelerometer connected, measure across its terminals at any point in the system. You should measure 10 - 14 volts. If not, you have an accelerometer or cable problem.

Jon
Spintelligent Labs