Philips EZ139 User manual

Underexposure display

or

Incorrect exposure display

or

Incorrect exposure early warning system

There are different reasons for the incorrect exposure display to come up:

1) An exposure has not been terminated as provided

1.1 during non-automatic exposures (normally terminated by mA-control)

- due to an exposure hand switch which has been released too early

- due to an interrupted exposure command of the system

1.2 during automatic exposures (normally terminated by dose rate control)

- due to an exposure hand switch which has been released too early

- due to an interrupted exposure command of the system

1.3 during automatic exposures prematurely terminated by the AEC fault exposure detection

1.4 due to a setting / system malfunction during TDC exposures

1.5 as one of the max limits have been reached (mAs or ms limit), see Appendix A

2) An error occurred which interrupted the exposure.

What happens with the data display on the control desk?

Exposure parameters of non-automatic exposures

kV-mAs kV-mAs-ms kV-mA-ms

remain in the control desk display as set.

The post-indication values of interrupted AEC (automatic exposure control) exposures

kV falling load (kV) kV fixed current (kV-mA) tomo density control (TDC)

remain on the display for 25 seconds, afterwards the set exposure values re-appear.

One can see the post indication values again after pushing the
flashing under exposure light first.

To figure out why the underexposure display is flashing one has to push the

If the underexposure display goes out after pushing the
reasons given at 1).
None of the reasons given at 1) lead to an error entry in the error log index, details to 1.x items next page.

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key once one has to look for one of the

key once, but one has to turn the

key.

If the

key has to be pushed twice to get the underexposure display off an error event

(case 2)) interrupted the exposure.

The first key stroke erases the error condition, the second one turns the underexposure display off.

Sometimes the error display disappears from the display, but one can see the error again after pushing the

key three times in a row.
If there is more than one error logged for the same event only the last one is displayed at the desk.
Check the error log index and look for individual or multiple entries.
Multiple entries are typically logged almost at the same time or with just one or a few seconds difference.
Check the error details afterwards and solve the problems.

Detailed explanation of exposure terminations leading to a flashing underexposure display:

1.1 Optimus generators terminate the non-automatic exposures once the set mAs value has been

achieved no matter which of the non-automatic techniques has been selected.
Function unit mA control EZ119 then sends the exposure off command.

> There must have been an external interrupt of the exposure command signal, e.g. let go of the
exposure hand switch.

> There must have been an interrupt of the system exposure command signal, e.g. the grid or
or tomo sweep contact.

> If FU mA does not terminate Central Unit EZ139 will finally do with a backup timer, but then there
will be an error code additionally to the flashing under exposure display.

1.2 If dose rate control does not terminate an AEC exposure

> There must have been an external interrupt of the exposure command signal, e.g. let go of the
exposure hand switch.

> There must have been an interrupt of the system exposure command signal, e.g. the grid or
or tomo sweep contact.

1.3 The AEC fault exposure detection terminates exposures if the dose signal coming in did not
increase a certain level which is calculated from the cassette speed and other APR parameters.
Detailed explanations in Optimus service manuals chapter FAULT FINDING.

> Malfunction of the measuring chamber or the cable connection to the generator back panel.

> APR settings (kV, cassette speed) and patient size don’t not match.

1.4 Identical functionality to 1.3, just for tomo with one exception:

> Attenuation of object too small. 0.5mAs and 1mA are smallest values. Once lower values are

requested by dose rate control the under exposure signal flashes.

1.5 See Appendix A.

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