Studies from the Autotrephon, I. Some Points in General Operation and Maintenance

Abstract

The Autotrephon, described in Stanley, 1951, though very carefully designed, is somewhat complicated, and the experience of two years has shown that there are some points with respect to its operation and maintenance which should be placed on record. Warm-chamber controls. The setting of the thermostat for the humidifier heater (Stanley 1951, TH-3, Fig. 11) is very important. If it does not cut in and out within about 0..10 C., of the warm-chamber temperature, quite pronounced surges will occur in the temperature of that chamber. These will show as rather regularly spaced spikes or peaks on the temperature record. Under dry room conditions, where humidification is frequent, these spikes may run together to form a saw-tooth record. Dirty contacts on the warm-chamber thermostat (ibid., TH-1, Fig. 3) produce a very irregular variation in the temperature record. When the heater of the warm chamber (ibid., H, Fig. 3) operates, it causes a small rise of temperature (about 0.30 C.) in the air flowing down the lateral airchannels of the warm chamber. As the wet-bulb thermometer is set in this stream (ibid., WBT, Fig. 3), readings should not be taken when the heater is operating. A neon pilot light should be wired in parallel with the heater to act as an indicator. When running with the warm-chamber temperature very close to that of the surrounding room, it will be found that the chamber tends to control on the cooling system during the day, and on the heater at night. This produces a reiterated step effect on the record. This cannot be eliminated, but it can be minimized by making the differential on TH-1 as small as possible. The differential should be reduced to the point where the cooling system just fails to operate from the minute overshoot of the heating system. This will give a differential of perhaps 0.15 to 0.20 C. The differential of the humidistat (Ibid., Fig. 5) should not be set too fine, as the contact arm (ibid., CA, Fig. 12) naturally has a rather large swing. Experience is the only guide, but the total gap between the contact arm and the fixed contacts can be about 1/32 in. If the apparatus is shut down, the tension on the hairstrand should be released by turning the adjusting nut AN (ibid., Fig. 12) until the strand is limp. If this is not done, the hairs may break on a dry day. To prevent the hair-strand twisting when the adjusting nut is turned, a small cross-pin should be put through the rod R (ibid., Fig. 12). This should be located just where the end of the dotted pointer touches the rod, R, in Figure 12. It can be installed by sweating a brass sleeve (1/16 O.D.) over R, and drilling through this assembly, and sweating in a 34-in. length of piano wire. If this wire is held between finger and thumb of the left hand while AN is turned with the right, adjustments are readily made. The end-clips of the hair-strand were not clearly shown in Stanley 1951, and one is therefore shown herewith as Figures 1A and 1B. The clip should be milled out of non-thermoplastic bakelite, and cannot be re-used. The hairs are ordinarily human hair. We have not found that blond hairs are essential. The hairs need only be washed with ether prior to use, to wash off grease. Any good grade celluloid cement will do for cementing the hairs into the clip, but it is important that they be stretched evenly before cementing. This may be done by cementing into one clip, threading through the holes of the second clip, and hanging