Model 859A-1

The Model 859A-1-72 controller is used to drive the stepping motor located inside the Model 859-1-50 sampler. The motor control circuit receives a- 12 VDC signal from an unregulated power supply and converts it into pulses to sequence the stepper motor. The controller enables the operator to establish the speed of the moving filter. There are two methods used to set the speed in which the motor can be driven. One method is a rotary switch used to select a resistor-capacitor network. This network is used in conjunction with a 555 timer. The selectable speeds via the switch are: 0.5, 1, 2 or 10 inches per hour. The second method involves removing a jumper wire in the controller and allowing an external pulse to determine the filter speed. The jumper wire is normally connected to terminal points S and V inside the controller. By removing this wire, the 555timer is disabled. The filter-advance circuit is operated by a momentary pushbutton switch. When depressing the momentary pushbutton switch, the filter will advance for an adjustable pre-determined time period (factory set at 2 sec). The Model 859-1-50 sampler is designed so that when a radioactive effluent is being sampled, the effluent is directed against the slow moving filter paper. As the effluent passes through the filter paper, the particulates are trapped and their emissions monitored by the beta detector, Model 943-25T. The moving filter is wound on a take-up wheel for disposal purposes. Micro-switches are used to detect torn or low filter tape.

The Model 859A-1 Moving Particulate Filter Sampler with Controller is designed to collect and monitor radioactive particles found in airborne process streams. By using a moving filter monitor, the background radiation buildup and associated decrease in sensitivity associated with a fixed filter monitor is avoided. A vacuum pump, provided separately, provides the motive force needed to withdraw the sample from the source, and permits the radioactive particulates to be collected on the filter paper. Although normally supplied with a Model 943-25T Beta Scintillation Detector, the Model 943-15 Alpha Scintillation or Model 943-3X Series Gamma Scintillation Detectors may be used with the Model 859A-1 for alpha or gamma radioactivity monitoring. The Model 859A-1 may be used with either a Model 942A Digital Ratemeter or a Model 960 Digital Radiation Monitoring Systems Process Controller.