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Laboratory of Neuropsychology

Precision Liquid Dispenser

We have developed a precision liquid dispenser for accurate and repeatable computer-controlled delivery of water and thicker liquids. Calibration is in volume steps of 0.05 ml. Multiple units can be cascaded to deliver different liquids on a moment-to-moment basis. Detailed construction information is available on the link below. See the original article in Journal of Neuroscience Methods for a detailed description and commercial sources for this device.

Description

The liquid dispenser has three components (left-to-right in the photograph), the control unit, the reservoir unit and the solenoid. The control unit provides precisely-timed pulses to the solenoid. It also does communications, coordination, and monitoring. The reservoir unit operates on about 20 lbs of air pressure. It supplies pressurized liquid from the bottle reservoir to the solenoid. The solenoid delivers precise droplets of fluid. Although somewhat expensive to implement, the design is otherwise well-suited to deliver multiple fluids to the mouth of an animal, but stacking solenoids close together and providing a control unit and reservoir unit for each one. A manifold is used to combine the outputs of multiple solenoids.

The control unit does a large number of functions, from pulse timing to serving status web pages on a network. However, with the aid of a separate 24 volt power supply and solid-state relay, the reservoir unit and solenoid can be connected directly to a computer and operated without the control unit.

photo of liquid dispenser
Dispenser has three parts: control unit, frame for reservoir and remote solenoid.

Performance

The repeatability of the dispenser delivery mechanism can be seen in this pair of histograms plotted together. Using a fixed air pressure (5psi), a fixed solenoid opening time (14ms or 28ms), single droplets of distilled water were dispensed and weighed at room temperature. The droplet weights are tightly clustered around 0.054g (~0.054ml) and 0.116g (~0.116ml) of water. Other performance measures are described in the article.

chart showing distribution of water droplet weights for two solenoid times at 5psi

These data are based on the weights of single droplets dispensed by the unit.

Publication

Documentation