Claims
- 1. A method of varying a capacitance to compensate for stray capacitance in a transmitter in a two wire current loop having a fixed module which includes a capacitance pressure differential sensor for changing a capacitance C.sub.L and a capacitance C.sub.H in response to pressure, the fixed module adapted for connection to an analog removable module having an adjustable compensating capacitance M.sub.A C.sub.DA and resulting in a pressure transfer function: ##EQU8## and adapted for connection to a digital removable module having a compensating capacitance C.sub.DD and resulting in a transfer function: ##EQU9## the method comprising: providing a capacitance compensation circuit in the fixed module;
- creating a compensation capacitance C.sub.DM for the capacitance compensation circuit by placing an electrode in a cavity, the cavity filled with a dielectric material; and
- selecting C.sub.DM by changing the position of the electrode in the cavity so that when M.sub.A C.sub.DA equals C.sub.DD a pressure transfer function for the fixed module in combination with the analog removable module is substantially the same as a pressure transfer function for the fixed module in combination with the digital removable module.
- 2. The method of claim 1 including varying dimensions of the electrode to obtain the desired capacitance value for C.sub.DM.
- 3. The method of claim 1 wherein the cavity is formed in a housing of the transmitter.
Parent Case Info
This is a divisional of application Ser. No. 07/775,311, filed Oct. 18, 1991, now U.S. Pat. No. 5,237,285.
US Referenced Citations (13)
Divisions (1)
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Number |
Date |
Country |
Parent |
775311 |
Oct 1991 |
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