Emerson 00809-0100-4514 Rosemount, Reference Manual, P =, Constant ×, ⎛ C 2 - C 1⎞, Welded Seals

Rosemount 1154

Reference Manual

00809-0100-4514, Rev BA January 2008

K1	is a constant.
C1	is the capacitance between the high pressure side and the sensing
	diaphragm.

C2 is the capacitance between the low pressure side and the sensing diaphragm.

fVp – p	Iref
	= --------------------
	C1 + C2

Where:

Iref is the current source.

Vp-pis the peak-to-peak oscillation voltage.

fis the oscillation frequency.

Idiff = fVp – p(C2–C1)

Where:

Idiff is the difference in current between C1 and C2.

Therefore:

P =	Constant × I		= I	⎛ C2 – C1⎞
				⎜ --------------------⎟
		diff		ref⎝ C2 + C1⎠

Figure 4-1. The δ-Cell.

Leadwires

Isolating

Diaphragm

Capacitor

Plates

Sensing

Diaphragm

Rigid

Insulation

Silicone Oil

Welded Seals

4-2