An experimental setup for traceable measurement and calibration of liquid flow rates down to 5 nl/min

Abstract

This work presents the improvements of an experimental setup for measuring ultra-low flow rates down to 5 nl/min. The system uses a telecentric CCD imaging system mounted on a high-precision, computer-controlled linear stage to track a moving liquid meniscus inside a glass capillary. Compared to the original setup, the lowest attainable expanded uncertainty at any flow rate has been reduced from 5.4% to 2%. In addition, the conformity with specification of three commercial micro-fluidic devices was evaluated using the new setup: one syringe pump, one implantable infusion pump and one thermal flow sensor. The flow sensor and the implantable infusion pump met the compliance criteria (coverage probability 95%). The syringe pump however, failed to meet the specifications at 5 nl/min and 10 nl/min. No assessment could be made at higher flow rates.

Flowmetering for microfluidics

“…In response to the limitations of the gravimetric principle previously mentioned, investigations on the front tracking meniscus method were carried on by Lubeck University. 110,113 First investigated for low flow rate by Richter et al, 114 this method relies on tracking the meniscus displacement of a flowing liquid in a capillary of known dimensions set at the outlet of the calibration system, as described in Fig. 7.…”

“…On the left: Side view. 113 measurements and standardization. This is addressed by metrology, but there is still a delay and a performance gap between the development of flowmeters by academic and industrial players, and the development of primary standards within metrological institutes.…”

“…a) CCD camera, b) lens, c) LED, d) linear stage, e) capillary, f) mirrors, g) regulated chamber, h) heating element, i) vibration-free table, j) DUT, k) thermally-insulated fittings and tubing, l) valve, m) polymer tubing, n) PC. On the left: Side view 113.…”

Calibration of insulin pumps based on discrete doses at given cycle times

“…The position of the pump must be adjusted to the height of the meniscus of the oil layer in the glass vial [2,8], which is required by the standard IEC 60601-2-24:2012 [4]. The optical method is the front track of the meniscus of a liquid in a pipette or a capillary, using the position of the meniscus as a function of time to determine the displacement and its corresponding volume of one or several consecutive doses [6,7,9,10]. Another optical method is to determine the volume of a liquid sphere attached to the cannula.…”

Low liquid flows – an important aspect in medical technology

“…In addition to the common gravimetric method, new methods are discussed that could be applied for extremely low flows in case the gravimetric method is not suitable. This includes an optical front tracking method [1] and flow sources. One source based on volume expansion is introduced in [9].…”