| 摘要 |
An electrovalve (EV3) is fitted between a second electrovalve (EV2) and the means of pipetting (AP). The pipetting cycle includes drawing up rinsing liquid into two working chambers. A transition phase has a first valve (EV1) open; a sampling phase has a second valve (EV2) closed and a third valve (EV3) open, and the sampling phase ends when the third valve is closed There are at least two pumping units (1, 2) of different capacity, each with a cylindrical cavity (AL1, AL2) with an impermeable piston rod assembly (TP1, TP2) sliding inside to define a working chamber whose volume varies as a function of the axial position of the piston. The ends of the piston rod assembly which protrude from the cavity are coupled to an activator driven in rotation by a common motor (MO, MP). The working chamber of each pumping unit is connected to a circuit containing successively a pipe opening into a rinsing liquid reservoir (RL), two electrovalves (EV1, EV2), and a section of circuit connecting the second valve to means of pipetting. The larger working chamber is in the part of the circuit ensuring a link between the two valves and the second working chamber is connected to the above-mentioned section of circuit via a linkage. The valves and the motor are controlled to obtain a sequence in which the motor reverses continuously to draw up rinsing liquid into the two working chambers. During the pipetting cycle, from the transition phase, the first two valves are open until the third valve is closed and, at the end of the sampling phase, the third valve is closed and the second valve is open. The pipetting cycle includes a back-washing phase during which the motor turns forwards to cause a back-washing of rinsing liquid in the two chambers. This includes the following phases: a transition phase where the third valve is closed whilst the first two are open to allow the rinsing liquid to back-wash continuously in the chambers to the receiver; a back-washing phase in which the third valve is open and the second valve closed: the first valve remains open to allow the product to back-wash the analysis receiver, and the back-washing ends when the third valve is closed and the second valve opened: the first valve remaining open throughout. The first valve can be closed when the second and third valves are open and the motor is stepped to backwash the rinsing liquid in the two syringes in the direction of the means of pipetting. The pipetting cycle includes a return to zero phase where the chamber are filled with the rinsing liquid, the first two valves are open and the third is closed, the motor turns backwards to pull the pistons back to the zero position and air is then evacuated from the means of pipetting by opening the second and third valves and closing the first while running the motor forwards to push the rinsing liquid towards the means of pipetting and bring the pistons into a rest position. The chambers are made in the same cylinder block and their upper sections are conical. The motor (MP) drives a pinion (PN) engaged in a rack (CR) fixed to the piston rod assembly. The valves are controlled by a processor (MC) which receives data from an optical reader connected to the rack, giving the position of the piston assembly. |
