Reliable, Inexpensive, Transistorized Liquid Nitrogen Level Controller H. Seguin, R. W. Leonard, and J. Imae Citation: Review of Scientific Instruments 37, 1747 (1966); doi: 10.1063/1.1720111 View online: http://dx.doi.org/10.1063/1.1720111 View Table of Contents: http://scitation.aip.org/content/aip/journal/rsi/37/12?ver=pdfcov Published by the AIP Publishing Articles you may be interested in An Inexpensive Automatic Liquid Nitrogen Level Control System Using an Integrated Circuit J. Vac. Sci. Technol. 8, 424 (1971); 10.1116/1.1314477 Simple, Inexpensive, Transistorized, Continuously Monitoring Liquid Helium and Liquid Nitrogen Level Indicator Rev. Sci. Instrum. 37, 1743 (1966); 10.1063/1.1720109 Inexpensive, Nonelectrical, Liquid Nitrogen, Constant Level Control System for Ultrahigh Vacuum Trapping Rev. Sci. Instrum. 35, 1082 (1964); 10.1063/1.1718944 Liquid Nitrogen Level Control Rev. Sci. Instrum. 30, 598 (1959); 10.1063/1.1716698 Liquid Nitrogen Liquid Level Controller Rev. Sci. Instrum. 30, 371 (1959); 10.1063/1.1716629
This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitationnew.aip.org/termsconditions. Downloaded to IP: 129.101.79.200 On: Tue, 09 Sep 2014 18:24:08
1747
NOTES Because of the high degree of mechanical and electrical stability of the device, it was found that relative mechanical displacements could be measured to approximately SO A over a dynamic range of some SO p,. The maximum departure from parallelism of the reflector as it translated was found to be less than 2" for a maximum displacement of SO p" while over the first 25 p, the nonparallel ism could not be detected. It was felt that the very slight nonparallelism observed at larger displacements was generated by the particular lever type linkage used and not by the diaphragm displacement mechanism itself. Notwithstanding, the accuracy and range of travel obtained are remarkable considering that the diaphragms were made only 2! cm in diameter. It should be possible, therefore, to obtain even less nonparallelism over far greater translations by building a larger version of this device.
trigger as the switching element. This device shown in complete schematic in Fig. 1 used a simple! W carbon resistor Rl inserted through the wall of a thin stainless steel tube as the level sensing element. The top of the sensing probe assembly was kept at a reference temperature by means of connection to a large room temperature heat sink. Sensitivity of the sensing resistor was then adjusted through the use of a variable resistor potentiometer combination R2 and RlO while the degree of liquid level regulation was set by potentiometer R3, which determined the Schmitt hysteresis. Biasing of the Schmitt trigger, formed by transistor Ql and Q2, was designed to provide a failsafe feature such that if the sensing element became open circuited or otherwise inoperative, the relay driving transistors Qa and Q4 were automatically cut off, thus preventing any accidents. The power supply for th,e Schmitt trigger was well regulated with Zener diodes to insure consistency of switching level. During operation, a double acting solenoid operated air valve applied air pressure to the nitrogen reservoir Dewar, thereby forcing the liquid nitrogen up a transfer tube into the nitrogen jacket of the helium cryostat. "Filling" and "standby" pilot lamps were included in the circuit design to provide visual indication of the operational status of the level controller. In addition, a bypass switch was also included for manual operation. The device has proved to be very reliable and suitable for continuous duty.
* Supported in part by the Office of Naval Research.
P.Z.T.4 is the trade name for a lead zirconate-Iead titanate piezoelectric ceramic, manufactured and distributed by Piezoelectric Division of Clevite Corp., 232 Forbes Road, Bedford, Ohio. 2 J. K. Clapp, Physics 47,712 (1928). 1
Reliable, Inexpensive, Transistorized Liquid Nitrogen Level Controller* H.
SEGUIN,
R. W.
LEONARD, AND
J. IMAE
Physics Department, University of California, Los Angeles, California 90000 (Received 27 June 1966; and in final form, 12 August 1966)
A SELF-CONTAINED liquid nitrogen level controller having positive switching action without jitter was designed and constructed utilizing a transistorized Schmitt
* Supported in part by the Office of Naval Research.
r=-:-=--'-~'-----
HEAT/' SINK
M ' I ' v - _ - B + 18 V. D.C. lN483
'-------
This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitationnew.aip.org/termsconditions. Downloaded to IP: 129.101.79.200 On: Tue, 09 Sep 2014 18:24:08
1747
NOTES Because of the high degree of mechanical and electrical stability of the device, it was found that relative mechanical displacements could be measured to approximately SO A over a dynamic range of some SO p,. The maximum departure from parallelism of the reflector as it translated was found to be less than 2" for a maximum displacement of SO p" while over the first 25 p, the nonparallel ism could not be detected. It was felt that the very slight nonparallelism observed at larger displacements was generated by the particular lever type linkage used and not by the diaphragm displacement mechanism itself. Notwithstanding, the accuracy and range of travel obtained are remarkable considering that the diaphragms were made only 2! cm in diameter. It should be possible, therefore, to obtain even less nonparallelism over far greater translations by building a larger version of this device.
trigger as the switching element. This device shown in complete schematic in Fig. 1 used a simple! W carbon resistor Rl inserted through the wall of a thin stainless steel tube as the level sensing element. The top of the sensing probe assembly was kept at a reference temperature by means of connection to a large room temperature heat sink. Sensitivity of the sensing resistor was then adjusted through the use of a variable resistor potentiometer combination R2 and RlO while the degree of liquid level regulation was set by potentiometer R3, which determined the Schmitt hysteresis. Biasing of the Schmitt trigger, formed by transistor Ql and Q2, was designed to provide a failsafe feature such that if the sensing element became open circuited or otherwise inoperative, the relay driving transistors Qa and Q4 were automatically cut off, thus preventing any accidents. The power supply for th,e Schmitt trigger was well regulated with Zener diodes to insure consistency of switching level. During operation, a double acting solenoid operated air valve applied air pressure to the nitrogen reservoir Dewar, thereby forcing the liquid nitrogen up a transfer tube into the nitrogen jacket of the helium cryostat. "Filling" and "standby" pilot lamps were included in the circuit design to provide visual indication of the operational status of the level controller. In addition, a bypass switch was also included for manual operation. The device has proved to be very reliable and suitable for continuous duty.
* Supported in part by the Office of Naval Research.
P.Z.T.4 is the trade name for a lead zirconate-Iead titanate piezoelectric ceramic, manufactured and distributed by Piezoelectric Division of Clevite Corp., 232 Forbes Road, Bedford, Ohio. 2 J. K. Clapp, Physics 47,712 (1928). 1
Reliable, Inexpensive, Transistorized Liquid Nitrogen Level Controller* H.
SEGUIN,
R. W.
LEONARD, AND
J. IMAE
Physics Department, University of California, Los Angeles, California 90000 (Received 27 June 1966; and in final form, 12 August 1966)
A SELF-CONTAINED liquid nitrogen level controller having positive switching action without jitter was designed and constructed utilizing a transistorized Schmitt
* Supported in part by the Office of Naval Research.
r=-:-=--'-~'-----
HEAT/' SINK
M ' I ' v - _ - B + 18 V. D.C. lN483
'-------
