Simple Continuous Electronic Readout for Rotameter-Type Fluid Flow Measuring Devices Using a Photoelectric Transducer Seymour Lowell and Stewart Karp C . W . Post College, Long Island University, Greenvale, N . Y . I1548 ROTAMETER-TYPE FLUID FLOW measuring devices are used extensively in laboratory as well as in engineering applications. In the laboratory, they are found incorporated in such instruments as gas chromatographs, atomic absorption and flame photometers, and many others. Rotameters readily lend themselves t o use in a variety of bench experiments involving gas or liquid flow. I n many instances a continuous and/or remote readout giving a n electronic signal which can be recorded would be desirable. This report describes a simple modification of rotameters which provide such a readout. Other modifications have been suggested to us, but they are not continuous or not so simple ( I ) as the one described here. Basically, a rotameter consists of a transparent glass tube with a tapered bore vertically positioned with the wide end up. The tube length and bore diameter are chosen in accordance with the nature of the fluid and the flow rate range of interest. A ball or other shaped “float” of appropriate size and density rides up and down the bore as a function of the fluid flow rate. The height of the float in a well designed tube is almost linearly related to the flow rate. Calibration is required, however, for accurate work. Our modification consists of mounting a light source near one end of the tube so that light rays strike the tube obliquely over its entire length, and mounting a photo-sensitive cell a t the other end of the tube. Figure 1 is a n example of such a setup. The device operates as follows: Light entering the tube is refracted and reflected along the bore toward the photocell. The light reaching the photocell is light which entered the tube between the float and the photocell. Light entering o n the other side of the float is effectively blocked by the opaque float. For a given geometry and fluid, the amount of light reaching the photocell depends upon float position-hence, upon fluid flow rate. Most commercially available rotameters can be modified by simply drilling a hole in one of the mounting blocks directly in line with the rotameter tube (see Figure 1) and cementing a photocell over this hole. Light striking the sides of the photocell can be avoided by recessing the cell into the block or simply by blackening it with paint or tape. The light sourcegenerally a convenient 12-V lamp-can be mounted with a n insulated clamp or soldered directly to the rotameter casing if the casing can be used as a lead to the bulb. We used a 12volt bulb powered by a suitable stable power supply. Electronic output suitable for use with a potentiometric recorder can be achieved with the Wheatstone bridge circuit as shown in Figure 2. If the photocell is mounted at the bottom and the light source near the top of the rotameter tube, the resistance of the cell decreases as flow rate increases. The position of the bulb and photocell can be reversed and in this case, the signal will also be reversed but no less useful. The optimum position for the light source depends on the geometry of the rotameter tube, but it is usually such that the filament is within ‘/z to 1 cm from the tube. This position (1) D. H. Fuller, U. S. Patent 2,912,858 (1959). 492
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12v. L A M P
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RECORDER
’-----FLOAT
Figure 2. Schematic circuit diagram
1. Full wave rectifier (International Rectifier 18DB4A-C or equivalent). 2. Photo cell (Clairex CL5M5L or equivalent). 3. Appropriate voltage divider for recorder or meter, RI = 5 MQ, R Z = 50 ka
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BALL POSITION
Figure 3. Typical calibration curve
is easily found by moving the bulb until maximum signal is obtained when the float is at some position in the tube. The relation between output and flow rate or ball position is not linear; therefore, calibration is required. Curves relating ball position to flow rate are usually supplied by the manufacturer for a variety of fluids and pressures. These curves can be used for the modified rotameter, if only a calibration curve relating output with ball position is determined. Hence, usually only a single calibration curve need be determined. Figure 3 shows a n example of such a curve. No change has been observed in the calibration curve of a modified rotameter over a period of a few months. Rotameters modified as described here have been used in our laboratory to monitor a variety of gases and aqueous solutions, some moderately colored. It has also been found that extremely low gas (probably low
modification of a basic rotameter-type flow device to provide an electrical signal for monitoring fluid flows.
liquid) flows can be monitored if the photocell is placed at the bottom of the tube and the light source is placed a centimeter or two from the bottom of the tube. Flows as low as 0.01 cc/min were easily monitored with gas rotameter tubes not designed for such low flows. In summary, this report describes a simple, inexpensive
RECEIVED for review September 21, 1970. Accepted October 29, 1970. This work resulted from a project supported by Quantachrome Corp., Greenvale, N. Y.11548.
Low Cost Parallel-to-Serial Converter for Digital Instrumentation Morteza Janghorbani, John A. Starkovich, and Harry Freund Department of Chemistry, Oregon State University, Corvallis, Ore. 97331 COMMONLY AVAILABLE LABORATORY digital instruments, such as digital voltmeters, typically store information in parallel binary-coded-decimal (BCD) form. Long term storage of such data on paper tape, magnetic tape, or direct processing by a computer frequently requires conversion of the data into a serial form. Typical commercial units may cost between $1000 and $2000, and are usually designed as part of more complex subsystems, with special input-output characteristics that may not be readily compatible with common digital instruments. A relatively low cost, yet versatile converter, was designed using readily available TTL logic IC’s. Specifically, Figure 1 shows a block diagram of the converter employed to interface a chemical instrument supplying parallel BCD data with a teletype requiring serial ASCII Code. The parallel-to-serial converter accepts BCD data from the output of the chemical instrument aia a DIGIT SELECTOR section. The parallel BCD data are then serialized, encoded, and are outputted cia the OUTPUT STAGE onto the storage device. Figure 2 presents a functional diagram of the parallel to serial converter. The heart of the converter consists of three 4-bit static shift registers (Fairchild, U6B930051X) which function both as serializer and ASCII Encoder. The BCD-outputs of the chemical instrument are hard wired to the appropriate inputs IN1 to IN8; IN1 corresponding to the most significant digit. IN9 is wired to generate the BCD representation of an ASCII blank (space). IN1 thru IN9 each contains a quad 2-input A N D gate (Motorola, MC3001P) and four high speed diodes (1N662 Jan). The four outputs of each of the quad AND gates are hard wired by means of the diodes to the four inputs of the shift registers PI thru Pl, the most significant binary bit (23) being connected to P4. Po and P 5 thru PI1of the registers (not shown in Figure 2) are hard wired to 1’s or 0’s to provide the remaining bits of ASCII Code. Figure 3a shows the ASCII bit pattern for decimal three. When the start button is pressed (either manually or automatically) the data available at IN1 are fed to the inputs of registers and are shifted together with Po and Ps through PI1, one bit at a time at the clock rate of 9.1 milliseconds per bit to the output. After the 12 bits have been shifted out, the counter-decoder (Fairchild, U6A998979X and Fairchild, U6B930159X) counts up by one, making the contents of IN2 available to the registers and this cycling continues until the contents of IN9 have been serialized and shifted out. In automatic mode, the P-S converter is reset and placed in standby condition awaiting the next start pulse. The start signal (print command) is a 9-volt square wave whose duration is not critical. No stop signal is required. In manual mode, the entire scanning operation repeats continuously, with two temporary contact switches controlling start and stop operations. When the output is connected to a teletype, each cycle results in the print-out of eight digits followed by a space. A
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