LM6000 pressure measurement uses absolute (PSIA) values for control. As abs = atmospheric+gauge

For calibration of transmitter what value to be used for atmospheric pressure? we used to take 14.696 PSIA (sea level) but OEM recommended we use actual values from barometer. we used actual and machine started behaving different. it gained some 5% load at same conditions.For 48.408 MW machine 2 MW is a big value.

All Inlet pressure CDP used PSIA values something happened???

If the machine absolute values are reading a little low how will machine behave.

 

Kevin Arnold,

It all depends on how the inputs are configured. Many turbine control systems used on GE turbines have a barometric (atmospheric) pressure transmitter (or multiple redundant transmitters) connected to the control panel, and the barometric pressure is added to the gage pressure signals from other transmitters. In other words, most pressure transmitter inputs will be calibrated and configured for gage pressure, and those signal(s) which require an absolute pressure will have a barometric pressure signal (appropriately converted) added to them, so that the actual, ambient pressure is being used to "bias" the signal(s).

Sometimes there is no ambient pressure transmitter, and in that case one has to consider what the elevation of the site the turbine is located is and use that value for calibration purposes. It would be best to know, during any calibration of this type of transmitter (one using absolute pressure) if there is a large difference between the typical ambient pressure (based on site elevation) and the current, actual ambient pressure because that may have some effect on the transmitter calibration.

But, in general, most turbine packagers will provide ambient pressure transmitter input(s) to the turbine control system when using absolute pressure to bias critical signals. And, if it's really critical they will usually provide redundant transmitters and choose the high or median value (as appropriate) of the multiple signals to use as the bias for the critical signals.

If the packager or OEM did not provide such ambient pressure transmitter(s), then it will be necessary to take the site elevation into account, as well as the actual ambient pressure at the time the calibration of any absolute pressure transmitter is being done, when calibrating the absolute pressure transmitter.