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Insight

Building a Time-Metered Dosing System

Accurate and precise dispensing of liquids is essential in a wide variety of industries, whether for scientific research, medical diagnostics, or high-tech industrial applications.

The ability to move these liquids repeatedly, and reproducibly, is essential to creating successful liquid handling systems.

Time-metered dosing, uses air to pressurize a reservoir, and a fast acting valve to precisely control the quantities of a liquid being dispensed.

By combining the high level of pressure control provided by the disc pumps, and the ultra-fast and consistent operation of The Lee Company VHS® valves, we have built a prototype of a compact (100x90x20 mm), low weight (<50 g) time-metered dosing system as proof-of concept, outlined in the AN059: Time-metered dosing – Disc Pump Application Note.

The application note outlines the following:

  • The basic design and operation of a time-metered dosing system
  • Priming and operating the time-metered dosing system
  • Data from a prototype system
  • In-situ set up of the system

For a quick summary of the basics and key takeaways please see below.

Primary Components

A disc pump
Smart Pump Module mounted with a disc pump
VHS® Valve
A disc pump, mounted as a Smart Pump Module
  • The disc pump’s fast response and pulsation-free output allow for a high level of pressure control. The disc pump can very accurately hold a target pressure above the fluids, the dispensed volume is then controlled by the accurate head pressure and opening and closing of the VHS valve for a defined length of time.
  • Using the disc pump mounted as a Smart Pump Module enables closed loop pressure control, and the speed of response ensures that the desired pressure / flow profiles are followed accurately/ The integrated drive electronics allow all components of the module to be controlled remotely with software we provide for free on our website.
VHS® SERIES 2-WAY DISPENSE SOLENOID VALVE
  • The VHS® Series 2-Way Dispense Solenoid Valve is a 2-way, 6 mm dispensing valve that combines inkjet printing technology with inert materials to achieve precision droplets in the nanoliter to milliliter range.
  • With an ultra-fast response time (as fast as 250 µs), it is ideal for accurate fluid regulation and dispensing repeatable droplets with minimal satellites.
  • The valve’s small size enables mounting in tight spaces, even in arrays directly above a well plate. It is offered with integrated precision orifices, nozzles, screens, or with our MINSTAC® connectors to vary the outlet nozzle and connect tubing.

Results

The graph to the right shows the average water droplet mass achieved for a range of reservoir pressures (Pr) and valve on-times (td). As the droplets are small (~ uL), measurements reported are based on the average droplet mass as measured using a 3 decimal place mass balance.

“A coefficient of variance (CV) of ~ 4% was demonstrated at dose sizes of 10 mg (10 uL), and at smaller dose sizes this value is believed to be limited by the resolution of the mass balance used in this demonstration.”
Key Takeaways:
  • Exciting opportunities lay ahead as we explore a wider dosing range with better instrumentation – we are actively involved in projects using droplet analyzers to produce future literature and guidance on this topic. We are looking to characterize the dispensing precision of dosing sizes smaller than 10 uL by eliminating current measurement limitation.
  • The compact nature of the system (100x90x20 mm) will prove a huge asset when miniaturizing and commercializing systems – improving not only the end user experience, but also the time to market and commercial viability of a system.
  • New, lightweight (<50 g) pressure driven systems such as this can unlock a new generation of untethered, automated, tightly integrated liquid handling devices. Current benchtop equipment for pressure driven flow systems often need separate pumps, pressure regulators and sensors and can be very heavy and bulky, weighing several kilograms.

For further information on system set up and results, please see AN059: Time Metered Dosing – Disc Pump Application Note.