Automatisierung und Mikrosysteme
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For a growing number of applications in microfluidic environments it is important to generate fluid streams with a minimum of pulsation. By their good pulsation characteristics and the PID-controlled drives the high-precision syringe pumps of neMESYS series are highly qualified for this application fields.
How can this good pulsation characteristic be reached? The following features are setting off the neMESYS dosing units against conventional syringe pumps or diluters and ensure an almost pulsation-free generation of fluid streams:
| conventional | neMESYS | |
|---|---|---|
| drive | stepper drive | servo drive |
| position control | unregulated | closed loop PID control |
| velocity control | steady velocity | closed loop PID control |
| linear unit | standard | high-precision-axis (1 mm pitch) |
| spindle drive | standard | ball screw drive |
| gear ratio | none | up to 29:1 |
| pulsation characteristics (dosing of a fluid stream of 5 µl/s with fluorescent colouring) pictures: Friedrich-Schiller-Unversity Jena | ![]() |
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The precision and the absence of pulsation was measured at the Institute for Physical High Technology in Jena by use of a technique for pulsation measurement in smallest fluid amounts.
For these measurements a flow sensor was used. This sensor consists of a micro channel with integrated heating element and temperature sensors, united in a small glass chip.
Six temperature sensors are arranged in flow direction symmetrically to the heating structure. The flow sensor uses the heat transfer coupled to a volume flow to gain the sensor signal.
For this purpose a defined energy is coupled into the fluid by the heater. This causes a symmetric temperature profile in the channel. If a volume flow is streaming through the measuring channel then it is coupled with a heat transfer. This causes an interference of the symmetric temperature profile in the channel. This disturbance variable is used for the measurement of the volume flow.
From the measured values the frequency spectrum can be determined by use of a Fourier transformation. From the graph of the spectrum it is possible to analyse at which frequencies there is pulsation.