DP cell
A DP cell is a device that measures the differential pressure between two inputs. Example: To measure the pressure difference between a container (or vessel) and the surrounding atmosphere, you may connect 'Hi' port of the DP-cell to a fitting that enters the vessel, using suitable tubing. The 'Lo' port, you leave open to the atmosphere (open air, or possibly through a buffer or desiccant chamber). The DP-cell will indicate the relative difference between the pressure of the vessel (container) and the atmospheric pressure. This signal is often wired to an indicator that reads out locally , or remotely in a control room, and/or as a control (or feedback) signal to a valve, pump, or other control element to maintain a set pressure, or limit a maximum pressure. Typically, the signal is 4-20 mA DC loop current, where, usually, 4mA represents the minimum differential pressure and 20mA represents the maximum differential pressure. . Alternatively, the signal may be a variable voltage, or digital information stream.