Topic ID: id_18718203
Version: 2.0
Date: Feb 4, 2020 1:39:43 AM

Auto Test and Manual Test

The difference between auto test and manual test is that the auto test feature runs a default number of iterations of each of the sub-tests, while the manual mode allows the user to specifically select a sub-test(s) and the number of iterations for that selection of test(s).

The following tests are executed during auto test (GUI shown in Figure 1):

Offset Drift
Pop/Noise & Microphonics
Offset & Noise

1 Offset Drift

A series of data collection scans, over a course of 120 seconds, and the offset means values are analyzed to measure the amount of variance over 120 seconds of scanning. There are 3 scans taken in a 4 x 5.00mm mode / Gain 31 and 3 scans in a 8 x 1.25mm mode / Gain 10 with a delay of 60 seconds between each scan. The absolute value of the Means are taken and compared.

There should be very little or no drift between the first scan of each scan mode and the scan taken 120 seconds later. The spec is ±3 counts for each channel across a 120 seconds time.

Table 1. Offset Drift Test
SCAN #	DAS GAIN	SCAN MODE	DESCRIPTION
1	31	4 x 5.00mm	Initial Offsets scan at specific technique
2	31	4 x 5.00mm	Offset scan after 60 second interscan
3	31	4 x 5.00mm	Offset scan after another 60 second interscan
4	3	8 x 1.25mm	Initial Offsets scan at specific technique
5	3	8 x 1.25mm	Offset scan after 60 second interscan
6	3	8 x 1.25mm	Offset scan after another 60 second interscan

Therefore, from Table 1 above, the difference in counts between scans 1 & 3 must be within 5.5 counts for 364-415 channels and 7.4 counts for 1-363, 416-768 channels, and also the difference in counts between scans 4 & 6 must be within 28 counts for 364-415 channels and 56 counts for 1-363, 416-768 channels. Failure analysis of the drift test may be a bad converter board, but also considerations need to be taken on account of room temperature fluctuations and DAS warm-up time. It may be normal for this test to fail if it is executed immediately after turning on the DAS.

2 Pop/Noise & Microphonics

A series of predefined rotating scans, w/o x-ray, and the scan data saved on disk for analysis. The scan data is then view averaged and the standard deviations are measured against a spec limit.

This test takes a series of three scans. In the auto-mode, it takes ten iterations of the series. Failure analysis of this test is dependent on test results. Pop/Noise and microphonics issues can be caused by many system related conditions. Some of the most common could be the DAS/Detector interface (such as elastomer connection caused by dirt, oil, debris), flex top cover clamp torque incorrect, air plenum not installed, fan orientation not correct, power supply noise, electrical connections, gantry rotation/mechanical issues, and external influences.

It is very important to look at patterns relative to DAS/Detector architecture, gantry rotation (azimuth position as well as velocity), and high voltage (with or without x-ray, rotor on/off).

Table 2. Microphonic Noise Scans
Scan #	Gantry Rotation	X-Ray	Rotor	Acquisition Mode	DAS Gain	Scan Time/VPS	Scan Data Saved
1	Rotating	No X-Ray	On	4 X 5.00	31	1 / 984	Raw
2	Rotating	No X-Ray	On	8 X 1.25	5	1 / 984	Raw
3	Rotating	No X-Ray	On	8 X 1.25	5	0.5 / 1640	Raw

Table 3. Microphonic Noise Spec Limits
			Channel Zones / Maximum DAS Counts Spec Limits
Scan #	Acquisition Mode	DAS Gain	1 - 64 705 - 750	65 - 224 561 - 704	225 - 560	751 - 762	763 - 768
1	4 X 5.00	31	33.2	24.0	18.5	40.6	29.5
2	8 X 1.25	5	119.0	81.6	63.0	142.3	119.0
3	8 X 1.25	5	119.0	81.6	63.0	142.3	119.0

3 Offset & Noise

This test collects DAS data with zero input current (no x-ray) and the mean value of each output channel is compared to spec. Also, the standard deviation is measured against a noise spec. It involves two scans, the first in a 4 x 5.00mm mode, gain of 31 and the other in a 8 x 1.25mm mode, gain 3.

Failure analysis is similar to that of DC Cal, with the exception that there is no input test voltage applied. Depending on failed pattern, based on DAS/Detector architecture, the fault may be a converter board, DAS/Detector interface, or power supply.

Table 4. Offset and Noise Scans
Scan #	Gantry Rotation	X-Ray	Rotor	Acquisition Mode	DAS Gain	Scan Time/VPS	Scan Data Saved
1	Stationary 0° Deg.	No X-Ray	Off	4 X 5.00	31	1 / 984	Raw
2	Stationary 0° Deg.	No X-Ray	Off	8 X 1.25	3	1 / 984	Raw

Table 5. Offset value - Analyze “Means - Raw”
			Channel Zones / Maximum DAS Counts Spec Limits
Scan #	Acquisition Mode	DAS Gain	1 - 64 705 - 750	65 - 704	751 - 762	763 - 768
1	4 X 5.00	31	420 ±70	420 ±70	420 ±70	420 ±70
2	8 X 1.25	3	930 ±200	930 ±200	930 ±200	930 ±200

Table 6. Noise value - Analyze “Standard Deviations - Raw”
			Channel Zones / Maximum DAS Counts Spec Limits
Scan #	Acquisition Mode	DAS Gain	1 - 64	64 - 704	751 - 762	705 - 750, 763 -738
1	4 X 5.00	31	15.4	13.8	19.4	13.8
2	4 X 1.25	3	57.2	47.0	65.4	57.2