X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Mon, 11 Apr 2011 07:56:57 -0400 Message-ID: X-Original-Return-Path: Received: from asmtpout022.mac.com ([17.148.16.97] verified) by logan.com (CommuniGate Pro SMTP 5.4c3j) with ESMTP id 4941626 for lml@lancaironline.net; Sat, 09 Apr 2011 17:56:18 -0400 Received-SPF: pass receiver=logan.com; client-ip=17.148.16.97; envelope-from=k.gregory@me.com MIME-version: 1.0 Content-type: multipart/related; boundary="Boundary_(ID_ZeFj/SgenDhCHjMuiY6BFg)" Received: from Tablet (ip68-108-134-119.lv.lv.cox.net [68.108.134.119]) by asmtp022.mac.com (Oracle Communications Messaging Exchange Server 7u4-20.01 64bit (built Nov 21 2010)) with ESMTPSA id <0LJE007AYNKVYA40@asmtp022.mac.com> for lml@lancaironline.net; Sat, 09 Apr 2011 14:55:44 -0700 (PDT) X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:5.2.15,1.0.148,0.0.0000 definitions=2011-04-09_08:2011-04-09,2011-04-09,1970-01-01 signatures=0 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 spamscore=0 ipscore=0 suspectscore=1 phishscore=0 bulkscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx engine=6.0.2-1012030000 definitions=main-1104090100 From: "K. Gregory" X-Original-To: brent@regandesigns.com X-Original-Cc: lml@lancaironline.net Subject: Thank you... X-Original-Date: Sat, 09 Apr 2011 14:55:42 -0700 X-Original-Message-id: <001001cbf700$dfab0960$9f011c20$%gregory@me.com> X-Mailer: Microsoft Office Outlook 12.0 Thread-index: Acv3AN8l4ef6mwSxTo+LCYRmMSxOsg== Content-language: en-us This is a multi-part message in MIME format. --Boundary_(ID_ZeFj/SgenDhCHjMuiY6BFg) Content-type: multipart/alternative; boundary="Boundary_(ID_bLPsgJl+Tr7L5hRgjMFAsQ)" --Boundary_(ID_bLPsgJl+Tr7L5hRgjMFAsQ) Content-type: text/plain; CHARSET=US-ASCII Content-transfer-encoding: 7BIT Sir, your efforts at explaining this to me are deeply appreciated. You are the first person I have found that could give me a clear and informed education on this problem. It is so concise yet thorough that I not only understand it, I am certain that you are correct. I would thank you more profusely, as you have been quite generous to me for supplying this, but I need to go fix some ground wires. Cheers (and thanks again dude), Kevin From: Brent Regan Sender: Subject: Re Request Electrical System Help Date: Fri, 08 Apr 2011 15:54:11 -0400 To: lml@lancaironline.net Message Header Undecoded Message Kevin writes: < The problem is likely NOT RF interference on the serial communication lines. The problem likely IS poor ground wiring. The hydraulic pump draws a lot of amps. All wire has resistance. Amps times resistance is volts so when the hydraulic pump motor is running the "ground" at the battery and the "ground" at the motor may be different by a several volts. Serial (RS232) 1communication uses a single wire that transitions from one voltage to another voltage to transmit data. The transmitter (sensor) and the receiver (EFIS) compare the signal to the LOCAL ground. If the ground voltage is different between the transmitter and the receiver then the signal may not be received. For example, say the receiver transmits 4 volts as a binary "1" and 1 volt as a binary "0" . The receiver interprets anything less than 2.5 volts as a 0 and anything more than 2.5 volts as a 1. If there is 2 volts of ground shift due to an induced voltage drop (the motor running) then the receiver will "see" the incoming signal changing from 3 volts to 6 volts, which it interprets as all 1s. A 1001101 transmitted message would be received as 1111111. Not good. Be sure that your EFIS display and all the sensors get their power and ground from the same point on the airframe. Good composite aircraft wiring systems have a single point that is the ground reference with all component grounds coming from this point. You do not want a ground wire run to another part of the airframe and then branching to different devices as the resistance of the wire will allow one device to effect the other. Power ground, signal ground and shield grounds must all be tied to the same point or else you will induce currents (AKA Ground Loops) in the ground wiring that will cause trouble. Even if you operate the EFIS off of emergency batteries, if a portion of the ground wiring between the sensors and the EFIS share a ground path with the motor then there will be trouble. As my friend Hamid Wasti says: "You must believe in one true Ground, because if you don't, it will smite you!" --Boundary_(ID_bLPsgJl+Tr7L5hRgjMFAsQ) Content-type: text/html; CHARSET=US-ASCII Content-transfer-encoding: 7BIT

Sir, your efforts at explaining this to me are deeply appreciated. You are the first person I have found that could give me a clear and informed education on this problem.

It is so concise yet thorough that I not only understand it, I am certain that you are correct. I would thank you more profusely, as you have been quite generous to me for supplying this, but I need to go fix some ground wires.

Cheers (and thanks again dude),

Kevin

 

From:

Brent Regan <brent@regandesigns.com>

Sender:

<marv@lancaironline.net>

Subject:

Re Request Electrical System Help

Date:

Fri, 08 Apr 2011 15:54:11 -0400

To:

lml@lancaironline.net

Message Header

Undecoded Message

Kevin writes: <<each time the gear motor runs, the output of the networked sensors (GPS, EMS, and ADAHRS) gets interrupted, resulting in red X’s displayed on screen. When the gear cycle is complete, the EFIS returns to normal. Testing with the EFIS system power isolated from the aircraft's electrical system by operating only on their independent backup batteries resulted in the exact symptom.>

The problem is likely NOT RF interference on the serial communication lines. The problem likely IS poor ground wiring. The hydraulic pump draws a lot of amps. All wire has resistance. Amps times resistance is volts so when the hydraulic pump motor is running the "ground" at the battery and the "ground" at the motor may be different by a several volts. Serial (RS232) 1communication uses a single wire that transitions from one voltage to another voltage to transmit data. The transmitter (sensor) and the receiver (EFIS) compare the signal to the LOCAL ground. If the ground voltage is different between the transmitter and the receiver then the signal may not be received. For example, say the receiver transmits 4 volts as a binary "1" and 1 volt as a binary "0" . The receiver interprets anything less than 2.5 volts as a 0 and anything more than 2.5 volts as a 1. If there is 2 volts of ground shift due to an induced voltage drop (the motor running) then the receiver will "see" the incoming signal changing from 3 volts to 6 volts, which it interprets as all 1s. A 1001101 transmitted message would be received as 1111111. Not good.

Be sure that your EFIS display and all the sensors get their power and ground from the same point on the airframe. Good composite aircraft wiring systems have a single point that is the ground reference with all component grounds coming from this point. You do not want a ground wire run to another part of the airframe and then branching to different devices as the resistance of the wire will allow one device to effect the other. Power ground, signal ground and shield grounds must all be tied to the same point or else you will induce currents (AKA Ground Loops) in the ground wiring that will cause trouble.

Even if you operate the EFIS off of emergency batteries, if a portion of the ground wiring between the sensors and the EFIS share a ground path with the motor then there will be trouble.

As my friend Hamid Wasti says: "You must believe in one true Ground, because if you don't, it will smite you!"

 

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