Flow rate

Last update: 2003/03/27

Master thesis
Doctoral dissertation
BOD sensor
Micro oxygen sensor
Paper-based oxygen sensor
Micro degasser
Micromixer
Flow rate
Dynamic Measuring Method
Fluidic MEMS packaging
Smooth Etching of Si
Standing Wave valve
IR aligner
World-to-chip Socket
Microfluidic socket 2
Socket2_English
PZT Spray Coating

Measuring microflow, in the order of ul/min, is a challenge to engineers. Traditional methods in macro world do not work simply because of lower signal/noise ratio.

One possible solution is to find a low noise measuring method. The other is to decrease noise level to 0. I choose the later one. Go digital!

AUTOMATIC MICRO FLOW RATE MEASUREMENT USING A MODIFIED COMPUTER MOUSE DEVICE

Zhen YANG and Ryutaro MAEDA

Fig. 1. The principle of detecting liquid in a glass tube using the difference of refractive indexes. Glass tube filled with gas disperses light (left) but it focuses light when filled with liquid (right). 

Abstract

An automatic system for measuring micro flow rate of liquid is presented. A computer mouse device was modified as an optical encoder for this purpose. All the sensing and electrical signal are processed by the mouse device. A very simple structure has been realized using the PS/2 mouse interface to get electric power and transfer the data to computer directly. The data treatment was programmed using the Microsoft Visual Basic. This system shows a useful solution for micropump’s evaluation. Because this device works in digital On/Off principle, there is no lower limit for measurable range of flow rate and bi-directional measurement is also possible. The full measurable range is up to 115 ml/min, at which the measurement precision is assured within ±2%. The resolution is depended on the sampling speed of computer (0.05 second). The device is not affected by the change of temperature or thermal capacity of fluids. It is an alternate as a tool to calibrate mass flow meter. Automatic parallel measurements in multi-channel are also possible. 

　FAQ

1. No response occurs when fluids pass the sensors 

I think your problem is the way to adjust the photodiode. On page 289, I wrote that I adjusted both the position of the glass tube and the sensitivity of PD. You can put a shutter with a small slit in front of the PD. or you use a filter (say a piece of paper) to decrease the light from LED. In my experiment, I just bent the PD/LED a little bit just as it response ON/OFF at air/liquid interface.

2. About precision

Basically, hardware is quite easy. The problem is the software. If you use Visual Basic, you can only get about 55 msec resolution, as I wrote in my paper. If you use C, you can have about 840 nsec resolution but problem still remain.