How to measure mas using the current clamp with TNT 12000

Transcription

1 How to measure mas using the current clamp with TNT Summary The Prova 15 amp clamp, when used with the TNT mas function, non-invasively measures the mas of X-ray generators. Introduction The Prova 15 amp clamp enables the TNT to measure the product of current and time (mas) in diagnostic X-ray systems without having a mechanical connection to the high-voltage transformer of the X-ray generator. The non-invasive method of mas measurements is utilized under the following conditions: 1. Access to ma taps for invasive measurements is not allowed, and 2. The X-ray manufacturer no longer supplies ma taps on their generator. Because non-invasive mas measurements use the magnetic flux associated with current through a wire, many external factors can affect the results and measurement of non-invasive mas such as the electronic noise from the rotating anode of the X-ray tube and the RF energy created in the highvoltage circuit of the generator. This interference can be minimized by proper placement of the amp clamp. Below are steps to take to ensure the successful measurement of mas non-invasively. Procedures Two procedures within application note: A. Using the hand-held display B. Using PC with Excel Add-in Note: this application note is a guide to obtaining repeatable results from your TNT with noninvasive mas clamp. No X-ray machines are alike; therefore the user is responsible for locating the optimal position of the Clamp and generator setting.

2 A. Using the hand-held display 1. Connect the Prove 15 clamp to either the TNT wireless detector or DoseMate dosimeter (must be enabled for mas) using ma cable assembly and BNC to double banana plug connector as shown below. Note: do not use ma shunt assembly with Amp clamp. 2. Establish connection between readout and mas function in TNT12000 Wireless Detector or Dosemate dosimeter as describe in the operators manual. 3. From the readout under the setup menu, select mas function as clamp. 4. Connect clamp to anode cable. Make sure the jaws of the clamp are completely closed around the cable. The direction of current flow through the clamp can be in either direction. Keep the controls of the clamp facing the user for ease of access. Pictured below are three possible connection points for the clamp. Note: the closer the clamp is to the generator, the more stable the results will be. Clamp at input to generator Clamp at opening of cable sheathing

3 Clamp at input to X-ray tube 5. Turn the dial of the clamp to the 4A range and press the zero button on the clamp. Note: ensure the red power LED is illuminated when the clamp is turned on. Note: the clamp must be zeroed every time it is moved. 6. At the readout, zero the mas meter. Close up of clamp at opening of cable sheathing 7. The display should indicate 0 ma and 0 mas. If not re-zero the clamp and the meter until the readings on the display are stable. 8. Set the generator for a technique that will result in a mas setting of greater than 5 mas. 5 mas is the minimum detectability of the TNT system. Typically, non-invasive mas reads low compared to control settings so the lowest technique should be 6.4 mas. 9. Make the exposure by first prepping the X-ray tube. Typically, there are two ways to initiate an exposure. The control console will have both a prep push-button switch and an exposure pushbutton switch. The exposure switch does not become active until the tube is fully prepped. The reason for the prep button is to heat the filament and get the rotating anode up to speed. The other configuration is a single two stage pushbutton switch where a slight press preps the tube and a full press makes the exposure. The spinning of the rotor will trigger a mas reading, which will be unstable and constantly changing for a few seconds. Disregard this and wait until the reading stabilizes before pressing the expose switch. 10. Fully depress the exposure switch to complete the exposure. 11. Once the exposure is made, the results will be displayed. Wait 2-3 seconds before releasing the exposure switch. When the exposure switch is released, a DC voltage is sent through the cable to stop the rotor from spinning. This could cause the mas clamp to trigger.

4 B. Using PC with Excel Add-in 1. Connect Prove 15 clamp to the TNT Wireless Detector or DoseMate dosimeter (requires enabled mas functionality) using the ma cable assembly and BNC to double Banana plug connector as shown. Note: do not use ma shunt assembly with amp clamp 2. Establish connection between PC and mas function in TNT12000 Wireless Detector or Dosemate dosimeter. 3. On the control bar of the add-in select ma input function as clamp. 4. Connect clamp to anode cable. Make sure the jaws of the clamp are completely closed around the cable. The direction of current flow through the clamp can be in either direction. Keep the controls of the clamp facing the user for ease of access. Pictured below are three possible connection points for the clamp. Note: the closer the clamp is to the generator, the more stable the results will be. Clamp at input to generator Clamp at opening of cable sheathing

5 Clamp at input to X-ray tube Close up of clamp from above picture 5. Turn the dial of the clamp to the 4A range and press the zero button on the clamp. Note: ensure the red power LED is illuminated when the clamp is turned on. Note: the clamp must be zeroed every time it is moved. 6. At the PC, zero the mas meter by clicking on zero ma on the control bar. 7. At this point the PC should not be indicating any exposures being made. If data is being registered by the add-in, re-zero the clamp and the meter. 8. Select the appropriate template from the add-in or use a blank worksheet, 9. Set the generator for a technique that will result in a mas setting of greater than 5 mas. 5 mas is the minimum detectability of the TNT system. Typically, non-invasive mas reads low compared to control settings so the lowest technique should be 6.4 mas. 10. Make the exposure by first prepping the X-ray tube. Typically, there are two ways to initiate an exposure. The control console will have both a prep push-button switch and an exposure pushbutton switch. The exposure switch does not become active until the tube is fully prepped. The reason for the prep button is to heat the filament and get the rotating anode up to speed. The other configuration is a single two stage pushbutton switch where a slight press preps the tube and a full press makes the exposure. The spinning of the rotor will trigger a mas reading that will be unstable and constantly changing for a few seconds. Disregard this and wait until the reading stabilizes before pressing the expose switch. The add-in will identify an exposure being made and record the values. At this point, tab up to the original cell where data should be stored. 11. Fully depress the exposure switch to complete the exposure.

6 12. Once the exposure is made, the results are displayed and the add-in automatically tabs down to the next cell. Wait 2-3 seconds before releasing the exposure switch. When the exposure switch is released, a DC voltage is sent through the cable to stop the rotor from spinning. This could cause the mas clamp to trigger. Waiting a few seconds after the exposure to release the exposure switch will lessen this effect. If this occurs, the add-in will identify this as an exposure, record the value and automatically tab down to the next cell. Before another exposure is made, use the up arrow key to tab to the appropriate cell.