Inspection
Inspect the unit after receipt for signs of physical damage. Report any damage to the carrier at once if any occurred in shipping.
Observe that tank pressure is within the 15-30 psi range. If the pressure is below 22 psi, the unit should be recharged. Refer to the Maintenance section.
Verification of the operation of the unit may be made with the aid of a digital voltmeter (DVM). Plug the line cord into the mains. Measure the output voltages from the BNC output connectors. All voltages should be less than millivolt with respect to ground. Operation may be verified by actual operation or by preliminary low-voltage calibration techniques.
The equipment setup depends on the tests to be performed and the auxiliary equipment used. Details are contained in subsequent paragraphs.
This section describes the proper techniques for the installation of the High Voltage Unit for calibrating or diagnostic investigation of an x-ray installation. The user is again cautioned about possible safety hazards due to the presence of high voltage x-ray radiation, and is requested to review the safety notice in the Preface.
Parts Necessary for Use
Two 12-foot long RG-58U cables with BNC connectors at each end for oscilloscope connections. (Supplied)
Besides the High Voltage Unit, the following parts are required:
- Two high-voltage cables, approximately 5 feet long with federal standard terminals at each end.
- Two federal standard dummy high-voltage receptacle plugs (Supplied)
- Two 1.5 oz. tubes of vapor-proofing compound for cables and plugs (Supplied)
- Small quantity of alcohol for cleaning high-voltage cable receptacles and terminals
- A piece of lead sheet 0.5 in. thick for blocking x-ray tube port, if no collimator is present
- A readout device such as a Dynalyzer digital display, DVM or Accu-Dyn+ system.
A differential input scope is not necessary as a composite A + C output is provided. Dual-trace or dual-beam capability is desirable to allow mA and kV to be viewed simultaneously.
Electrical Connections
The electrical interconnections are dependent on the test equipment used and the tests that will be performed. The High Voltage Unit can be used with a Accu-Dyn+ system, an oscilloscope, digital voltmeter or Digital Display.
Precautions
X-ray equipment is operated at lethal voltages. The operator must make certain that the main power switch is off when making or breaking connections in the high-tension circuit and that the cables are discharged before touching any high-tension lines.
Damage to the high voltage unit, the transformer, and the x-ray tube can occur if the cable plugs are not properly handled. Cable plugs are usually treated with silicone oil, transformer oil, or a vapor-proofing compound. This lubrication prevents corona or arcing from occurring in the receptacle. Oil is often used in vertically mounted receptacles while vapor-proofing compound is used in conditions where the oil could seep out, such as in the horizontal plans when cables are installed upside down. If the cables in an installation have some vapor-proofing compound on them, it would be in the best interest of system compatibility for the operator to insulate the cables from the Dynalyzer in a similar manner. If oil is used, and appears in to a depth of 1/8 in. in the receptacle, then additional oil is not necessary. Otherwise, add oil as necessary.
High Voltage Cable Connections
The Dynalyzer IV High Voltage Unit can be connected into the high voltage circuit in several ways. Each configuration implements the best method of measurement for the particular selected application. The following paragraphs outline these methods.
Series Connection (Figure 3)
This method is most often used since all x-ray exposure parameters attainable with the High Voltage Unit are measured e.g., Anode kVp, Cathode kVp, Anode + Cathode kVp, mA and filament current. The High Voltage Unit should be connected as close to the x-ray tube as possible (5-foot cables recommended) in order to properly observe the possible effects of cable charging during exposures of less than 100 mA. The High Voltage Unit may be located at the transformer when it is physically impossible to locate it close to the x-ray tube, bearing in mind the effects of cable charging.
Series Connection Anode Only (Figures 3 and 4)
The addition of a short high voltage cable necessary to complete the cathode circuit between the High Voltage Unit and the x-ray tube may have an adverse effect in certain situations, predominantly due to contact resistance. The added impedance of this cable and connections in the filament circuit may have a loading affect on the filament transformer. Therefore, when the Dynalyzer and short high-voltage cable is removed from the circuit, the filament current may increase resulting in an increase in mA which will in turn load the high tension transformer resulting in a lower kVp. The percent error will vary as a function of the loading characteristics of the filament transformer and high tension transformer as well as the total length of the high-voltage cables already in the circuit.
Because of this phenomenon, the following procedure is recommended:
- Use the shortest high-voltage cable jumper as physically possible between the High Voltage Unit and the x-ray tube (recommended length 5 feet).
- Insert both the anode and cathode sections of the High Voltage Unit in the x-ray circuit. (See Figure 3).
- For each desired measurement, record the anode kVp required to obtain the anode to cathode kVp at the mA of interest.
- Remove the cathode side of the High Voltage Unit from the circuit, leaving the anode side connected, and complete the circuit from the high tension transformer to the x-ray tube. (See Figure 4).
- Readjust the kVp and mA to precise values using the anode kVp readings and mA readings. This eliminates the effect of the added cathode cable insertion.
The setup as shown in Figure 4 may also be employed in grid-pulsed applications to accurately determine anode kVp and x-ray tube current. This technique does not measure cathode kVp or filament current because the cathode side of the Dynalyzer is not connected.
Series Parallel Connection
This method can only be used with x-ray generators having auxiliary high-voltage receptacles capable of simultaneous activation.
This setup shown in Figure 7 enables the measurement of all parameters except filament current and eliminates the possible adverse effect of an additional test cable in the filament circuit.
NOTE: The Dynalyzer IV has been designed for remote reading to minimize x-ray danger to the operator.
CAUTION: It is recommended that the High Voltage Unit and the Digital Display or oscilloscope (if used) be connected to the same grounded outlet or additional noise may be observed on the mA output.
Figure 3: ANODE X-RAY TUBE Series Connection
Figure 4: Series Connection Anode Only
Figure 5: Mammography Machine General
Figure 6: Mammography Machine Lorad/Hologic
Figure 7: Mammography Machine GE DMR Only
Figure 8: Connections