NAC459.622. Devices to control exposures.

     1. A means must be provided to terminate the exposure at a preset time interval, preset product of current and time, a preset number of pulses or a preset radiation exposure to the image receptor. In addition:

     (a) Termination of exposure must cause automatic resetting of the timer to its initial setting or to zero; and

     (b) It must not be possible to make an exposure when the timer is set to a zero or off position if either position is provided.

     2. A control must be incorporated into each X-ray system so an exposure can be terminated at any time except for:

     (a) Exposure of one-half second or less; or

     (b) During serial radiography when means must be provided to permit completion of any single exposure of the series in process.

     3. Each X-ray control must be located so that it meets the following criteria:

     (a) For stationary X-ray systems, and mobile and portable X-ray systems used as stationary X-ray systems, the control must be permanently mounted in a protected area. The operator shall remain in the protected area during the entire exposure.

     (b) For mobile and portable X-ray systems, the exposure switch cord must be at least 6 feet long.

     (c) The X-ray control must provide visual indication observable at or from the operator’s protected position whenever X rays are produced. In addition, a signal audible to the operator must indicate that the exposure has terminated.

     4. When an automatic exposure control is provided:

     (a) Indication must be made on the control panel when this mode of operation is selected;

     (b) When the X-ray tube potential is equal to or greater than 50 kVp, the minimum exposure time for field emission equipment rated for pulsed operation must be equal to or less than a time interval equivalent to two pulses;

     (c) The minimum exposure time for all equipment other than that specified in paragraph (b) must be equal to or less than one-sixtieth of a second or a time interval required to deliver 5 mAs, whichever is greater;

     (d) Either the product of peak X-ray tube potential, current, and exposure time must be limited to not more than 60 kWs per exposure or the product of X-ray tube current and exposure time must be limited to not more than 600 mAs per exposure except when the X-ray tube potential is less than 50 kVp, in which case the product of X-ray tube current and exposure time must be limited to not more than 2000 mAs per exposure; and

     (e) A visible signal must indicate when an exposure has been terminated at the limits described in paragraph (d), and manual resetting must be required before further automatically timed exposures can be made.

     5. With a timer setting of 0.5 seconds or less, the average exposure period (T) must be greater than or equal to five times the maximum exposure period (T max) minus the minimum exposure period (T min) when four timer tests are performed, for example, T 5 (T max-T min).

     6. Deviation of measured technique factors from indicated values of kVp and exposure time must not exceed the limits specified for that system by its manufacturer. In the absence of the manufacturer’s specifications, the deviation must not exceed 10 percent of the indicated value for kVp and 20 percent for exposure. All timers must be accurate to within ±20 percent of the selected value.

     [Bd. of Health, Radiation Control Reg. §§ 6.6.2-6.6.2.2.5, eff. 2-28-80]—(NAC A by R185-08, 5-7-2010)