2D-ARRAY warmup
The electronics of the interface, like any other dosimetry electronics, needs some time to warm up before readings are stable. PTW recommends a warmup time of five minutes. When an offset measurement is started right after the interface is turned on, readings will have considerable drift (up to 0.005Gy for a 60s measurement).
To find the ideal warmup time, I repeated the cycle offset measurement ("Zero", 60 seconds) and dose measurement ("Measure", 60 seconds) ten times, followed by an offset of 180s after a break and a measurement (M11) which serves as reference. Just to make it clear: all measurements were done without any radiation. These are pure drift measurements.
At T-15min, ARRAY and interface were taken out of a storage room (room temperature 17°C) and set up in an office (23°C).
| Time [mm:ss] | Action/Remark |
|---|---|
| 00:00 | Power up interface |
| 00:18 | Zero (60s) |
| 01:18 | Done |
| 01:23 | Measure |
| 02:23 | Done. Save as M1 |
| 02:35 | Zero (60s) |
| 03:35 | Done |
| 03:40 | Measure |
| 04:39 | Done. Save as M2 |
| 04:50 | Zero (60s) |
| 05:50 | Done |
| 05:54 | Measure |
| 06:54 | Done. Save as M3 |
| 07:05 | Zero (60s) |
| 08:07 | Done |
| 08:11 | Measure |
| 09:18 | Done. Save as M4 |
| 09:24 | Zero (60s) |
| 10:36 | Done |
| 10.39 | Measure |
| 11:40 | Done. Save as M5 |
| 11:45 | Zero (60s) |
| 12:48 | Done |
| 12:52 | Measure |
| 13:52 | Done. Save as M6 |
| 14:03 | Zero (60s) |
| 15:03 | Done |
| 15:15 | Measure (pressed "Start" 2 times -> CRC-error) |
| 16:15 | Done. Save as M7 |
| 16:30 | Zero (60s) |
| 17:26 | Done |
| 17:30 | Measure |
| 18:30 | Done. Save as M8 |
| 18:40 | Zero (60s) |
| 19:40 | Done |
| 19:43 | Measure |
| 20:44 | Done. Save as M9 |
| 20:55 | Zero |
| 21:55 | Done (60s) |
| 22:02 | Measure |
| 23:02 | Done. Save as M10 |
| 45:00 | Zero (180s) |
| 48:00 | Done |
| 48:05 | Measure |
| 49:05 | Done. Save as M11 (Reference) |
When starting the measurement at 15:15, I made a mistake: I pressed the Start button twice in short succession. MatrixScan reported a "CRC error", but started the measurement after I acknowledged the message. Interestingly, the result of the measurement M7 shows a negative dose peak of -0.002Gy (see enlarged image below). I have no explanation for this. Is it a coincidence? Has this something to do with the CRC error? Or was this some high negative energy cosmic ray particle? Maybe a tachyon? But this is not relevant vor the drift test.
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| Upper row (all images): Reference at 49:05. Lower row: T = 02:23. Strong stripe pattern. |
T = 04:39. Click on all images to enlarge. |
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| T = 06:54 | T = 09:18. Stripe pattern gets weaker. |
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| T = 11:40 | T = 13:52. Stripe pattern fades. Ideal warmup time reached. |
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| T = 16:15 | T = 18:30 |
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| T = 20:44 | T = 23:02 |
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| Isodose overlay of 02:23 (dotted) and 49:05 | Isodose overlay of 23:03 (dotted) and 49:05 |
Negative dose values may occur due to drift but negative isodoses are not displayed by VeriSoft.
Based on experience and these images, I recommend 10-15 minutes as warmup time. The duration of the offset measurement is taken as 60 seconds. Usually I repeat the offset measurement after another 10 minutes or so. Then all readings are absolutely stable.
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| Drift patterns (time is given in minutes after power up) |