15 Volt power supplies

From: "Cooper, Malcolm" <Malcolm.Cooper@ubht.swest.nhs.uk> Sender: owner-linac-eng@plato.aristotle.net To: "'linac-eng@plato.aristotle.net'" <linac-eng@plato.aristotle.net> Subject: re Elekta Power supplies Date: Thu, 09 Dec 2004 12:08:40 +0000

Hi there, Personally I would'nt change the limits as they are designed to pervent over/under voltages damaging the ic's. The +/-15v readback cycles through all the psu's so when yours dips it may not show on the item. I've found that the best way out is to change the faulty PSU .

The following note shows how to determine which PSU is faulty.Breifly look at the relevant item (+15v =I281) and part 130, The number in part 130 can be decoded to the relevent RTU. I find it wise to change both psu's as they are difficult to access.

The voltage monitor items continually monitor the voltages within the six control areas. When a problem occurs with the voltage in one of these areas the part 104 and 105 (104 =rtu 105=channel) are supposed to be frozen to indicate which RTU and channel is faulty. However, due to the queue system the part 104 and 105 can sometimes indicate the wrong value. There follows a brief description of how the items determine which RTU and Channel to look at and, perhaps, a more reliable way of determining which is at fault.

Taking +15v sys i281 as an example:

When part 130 is set to 19, the item looks at the process parameters, parts 131,132,133,134,135,136.in turn. A computation is then carried out on the values within these parts to determine which RTU and Channel is examined for information thus:

P130=19 p131=15393 p132=7201 p133=31777 p134=23585 p135=17375 p136=25567

value in pt 153
15393 = RTU 1 (ICCA B)
7201 = RTU 0 Ch. 97
31777 = RTU 3 Ch.97
23585 = RTU 2 Ch. 97
-17375 = RTU 5 Ch. 97
-25567 = RTU 4 Ch. 97

The same theory can be applied to all of the other monitor items ie i280 will access Ch. 96 (-15v sys ) of all six RTU's. If a faulty voltage is detected the value of the appropriate process parameter (p130's) being processed at the time is held in part 153. Applying the above calculation to this number will give the faulty RTU

NB if the +/- 15v and +5 v monitors point towards a particular RTU then the faulty PSU is on the opposite side. RTU1 is ICCA/B but the faulty PSU would be in ICCA/A.

Malcolm Cooper Ieng MIIE Linac Engineer Bristol UK