yee he erratic respors 2 mer ene aergen aa Oe cre ote at 6 1 tens ot eee he 88TEEa? met ea or TONESame“fetymin-aiscraft, Most monitors because of diffe: ences in ope railing 7: Yraciere preferred the \,/2DR-T1B ion chamber, and istics of V2Ci and Vide, Fics. the ve Fahive consequer'» riya portion of the stock of 247 pulse from V201 was not of sufficient amplitude instrumenis were used Service included reto trigger V101 consistently or the negative placement of 19 cnambers, 21 sets of batteries, pulse from V104 was greater than that from 5 meters, 5 battery switches, 5 tubes, and 8 V201 by a factor of from 5:1 to 30:1. Improved sets of minor parts and repair of 6 meter conoperation was obtained by carefully matching nection plugs. V201 and V104 tubes. It was also observed that The AN/PDR-T1B instruments were late in the capacity of cables W201 and W101 were arrival but were placed in service immediately causing losses of pulse height up to 80 per cent. after checking and calibration. All units reThis loss was considerably reduced by substiquired adjustment of calibration control as well tuting RG-78/v coaxial cable. Also by adding as grid current compensation potentiometers to two 224-volt Minimax batteries in series with correct for high readings. Attempts to set the the supply to V201, operation was satisfactory calibration control in the open resulted in in most instances. Full scale continuous or erratic readings, indicating a possibility that intermittent readings on all ranges and ‘‘hash” wind might build up a static charge on the chamin the headphones were rectified by inserting a ber surface. The case of this instrumentis 5-megohm resistor in the positive 700-volt well designed, and the instrumentis handy to supply between the vibrator and the VR tube, - wse and transport. These units were preferred Although the VR tube exhibited good regulating over all other types by most monitors. Some characteristics, the trouble would appear when difficulty was experienced in AN/PDR-TI1A units with chambers apparently leaking when the current exceeded 40 to 60 microamperes. Instruments with this fault were repaired by taken to high altitudes by plane. AN/PDR-T1B adding the 5-megohm resistor as noted above. models are equipped with reinforced chambers, In the majority of instruments the meter rewhich seem to reduce this trouble. Athough the AN/PDR-T1B is relatively watertight, considersponse was improved by increasing the time constant. This was done in several units by able trouble was experienced from moisture inserting a 2,000-ohm resistor in the meter inside the case when the instrument was excircuit in the “read” position. posed to much rain. Usually drying corrected this trouble. Evidence of their rugged con2.9.3 Ion Chamber Type Field Survey Instrustruction was shown when one instrument was On ments Instruments of the ion chamber type supplied were as follows: 47 Victoreen 247A, 40 Victo- reen 247E, 10 Victoreen 247H, and 60 AN/PDR- run over by a truck. The handle and a rear portion of the case were bent out of shape; the instrument still continued to operate satisfactorily. The meter movement in a numberof instruments was defective and required replacement or repair. Three such movements had open coils. Attention should be given the switch since this proved T1B. Construction and operation of all Victoreen instruments is much the same. The 247A and 247H instruments were used during Operation to be a source of trouble, resulting in erratic Sandstone, and previous reports have covered readings. Loose shaft bushings can also cause their operation. In general, the caSes are bulky with the center of gravity high, making them some- this erratic operation. Some of the batteries used are not of a common type and maybe difwhat difficult to handle and transport. The zero ficult to replace. If the instrument is handled setting drifts over a considerable length of roughly there is a tendency for the chamber to time before becoming stable, and the battery break loose from the supports. Several such current drain is high. Nevertheless the instruments have beenfield tested and are instances were noted. considered to be quite reliable. A number of 2.9.4 Alpha and Neutron Proportional Counters instruments were modified by drilling a small Four Pee Wee proportional counters for hole through the case and through the chamber. alpha detection were supplied as well as two This allowed their use at high altitudes, in airneutron detectors using modified Pee Weeinplanes, without danger of chamber collapse. struments with boron lined tubes encased in Calibration for pressure changes made them