Method of calibrating pressure measurement unit

A method of calibrating a pressure measurement unit in an extracorporeal circuit system, the pressure measurement unit including a container having an air chamber provided with an air inlet-and-outlet port, a liquid chamber provided with a liquid inlet port and a liquid outlet port, and a flexible diaphragm that provides a partition between the air chamber and the liquid chamber and that deforms in accordance with a pressure difference between a pressure inside the air chamber and a pressure inside the liquid chamber;

• a pressure measurer that is connected to the air inlet-and-outlet port of the container via a detachable connection;
• an upstream part and a downstream part of an extracorporeal circuit connected respectively to the liquid inlet port and the liquid outlet port of the liquid chamber;
• a closer that closes the upstream part and the downstream part of the extracorporeal circuit, respectively;
• a pressure adjusting pump provided in an extracorporeal circuit part closed by the closer or in a branch pipe branching from the extracorporeal circuit part;
• and
• a liquid sending pump arranged in the extracorporeal circuit,
• the method being performed when a connection between the pressure measurer and the air inlet-and-outlet port is disengaged after starting a pressure measurement for the extracorporeal circuit,
• the pressure measurer is connectable to the closed extracorporeal circuit part;
• and
• the extracorporeal circuit system further comprising a detector and a controller, the method comprising:
• detecting, by the detector, the disengagement of the connection between the pressure measurer and the air inlet-and-outlet port and transmitting information of the disengagement to the controller;
• stopping, by the controller, the liquid sending pump and closing the upstream part and the downstream part of the extracorporeal circuit using the closer;
• connecting the pressure measurer to the closed extracorporeal circuit part, measuring a pressure Pt of the closed extracorporeal circuit part and transmitting information of the pressure Pt to the controller;
• driving, by the controller, the pressure adjusting pump and setting the pressure Pt to a predetermined pressure P0, which is a pressure closer to the pressure at the time of starting the pressure measurement;
• and
• after the setting, disengaging the connection between the pressure measurer and the closed extracorporeal circuit part, and connecting the pressure measurer and the air inlet-and-outlet port to each other again.