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All about the SFM
How Does The Bio-Logic SFM Series Work?
The Bio-Logic Stopped-Flow Modules (SFM) are a fusion of technology, design and innovative control. Each element of the fusion compliments the others making the Bio-Logic SFM most powerful and flexible rapid mixing instruments existing today.
Principle of operation
All SFM instruments are based on an innovative use of stepping-motors to drive the syringes. With modern microprocessor techniques, stepping-motors offer control and power unmatched by any other fast driving system.
Each stepping-motor is controlled by one microprocessor enabling micro-positioning of the motor's rotor with an accuracy equivalent to 6400 steps per motor revolution; A volume precision of 30 to 200 nanoliter per micro-step. The damping produced by the rotor inertia results in a nearly continuous, linear movement of the syringe even at very low flow rates.
The high performance of each SFM and the high speed of the stepping-motors is achieved because of the quality of the power-supply.
Each Mixer Power-Supply (MPS) unit contains independent power-supplies for each syringe, each driven by their own microprocessor. The sequence of pulses sent to the stepping-motors is stored in the memory of each motor board. One main microprocessor board synchronizes all the power supplies, and communicates with the computer via a serial interface.
Stepping motors advantages
The use of stepping-motors and a high quality power supply, gives each SFM the following advantages.
- Completely Variable Mixing Ratios:
Because the flow rate and volume delivered by each syringe is independent of the others, mixing ratios are not fixed by syringes sizes. Mixing ratios are defined by the user, on-line. - Precise Flow Rate and Volume Control:
The flow rate and volume delivered by each syringe is chosen by the user, not defined by the instrument. - Reproducibility and Regularity:
The reproducibility and regularity of the linear translation of the syringes and the absence of pressure artifact allow optical recording during liquid flow.
This capability greatly facilitates the determination of the initial phase of the reaction being monitored during stopped-flow experiments and makes the equipment suitable for accurate, continuous flow experiments. - No Overpressure Artifacts:
Syringe movements are completely controlled by microprocessor and can be halted in a fraction of a millisecond. This abolishes the need for a stop syringe during stopped-flow experiments and eliminates the stop artifact present in most conventional stopped-flow systems. - Mixing of viscous solutions:
Syringe velocity is programmed and thus is independent of the solution viscosity. Very asymmetric mixing such as pure glycerol against water can therefore be achieved.
Mixer technology
The mixer is the heart of a stopped-flow instrument. Although being often referred as "T-mixer" a straight T-connection between 3 tubes is capable of mixing two solutions only in limited cases (aqueous solutions, symmetrical 1:1 mixing, limited range of flow rate). The mixer used in the Bio-Logic Stopped-Flow are all based on the "ball mixer" technology which is a proven design for creating turbulence in the most stringent conditions. Because of it the Bio-Logic Stopped-Flow can operate in a wide range of fluidic conditions such as : high dilution ratio (up to 1:100), high range of flow rate (from 1 to 20 mL/s), mixing of highly viscous solutions against water (viscosity up to 2000 centipoises or 2 pascal.second have been achieved).