An automatic device for controlling level of liquid nitrogen within two pre-set limits

✍ Scribed by H.L. Chhatwal; N. Chaudhuri

• Publisher: Elsevier Science
• Year: 1972
• Tongue: English
• Weight: 179 KB
• Volume: 12
• Category: Article
• ISSN: 0011-2275
• DOI: 10.1016/0011-2275(72)90117-8

✦ Synopsis

refrigeration power. Q' is linearly proportional to temperature difference AT = T o -T, where T o is the setting temperature and T is the actual temperature. For small AT, the input of the regulator Vi q is proportional to AT. IC-1 transforms Vin to (Vin + Vo)½ due to the square characteristic of diodes D21 and D22. V o is manually adjusted by a 10 turn helical voltmeter. IC 2 provides up to 200 mW of power proportional to Vin + V o to the 500 ohm heater, Diodes D23 , D24, D25 prevent reverse heater current flow, and so the whole system forms a linear feed-back system. The helipot allows an independent adjustment of the average heater power Qo so that the bridge is almost balanced. This feature also allows the system to return to a certain temperature after a temperature change.

The meter deflection of the regulator is proportional to the square root of the heater current so no switch is required to change the meter sensitivity.