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Re: MD485's_Campbellsci论坛问答

oceaner 0 94 次浏览 仪器使用

I have two CR1000's which are linked by MD485's. Communication has been perfect for several months since deployment. Now the communication link is working on an intermittent basis at best. The CR1000's are approximately 1500' apart. Both CR1000's seem to be working properly and I have made a direct connection at each logger with a PC and I can not connect to the other logger via MD485.

I checked the wiring I could easily access and it seems ok. My hunch is that the cable between the two MD485's has been compromised. But changing the wire will require a lot of work, even for testing purposes. It is suspended in a forest canopy (don't ask).

Re: MD485's_Campbellsci论坛问答

So I'm looking for ways to locate the source of trouble. I'm thinking there are three possibilities.

1.) The cable is bad
2 & 3, there is a problem with the CR1000 and or the MD485's

I'm thinking of swapping the MD485's with different ones.

I'm using shielded twisted pair(2) wire, with the shield connected at one end to earth ground. I also have a ground connection between the G connections on MD485.

Thanks

新对话如下：

Hi GeodeNZ,

If it's possible bring the two stations temporarily together with a new cable and test the communication.

My vote is on the bad cable.

The weak link has always been the cable. Those varmints will do a tight-wire routine and chew on the cable to sharpen their teeth.

Here is a company that makes deterrents for these reasons. It's safe for the environment and the varmints.
http://www.sniffnstop.com

I guess I should add that if you have some type of a wave generator like TDR. You could inspect the wire electronically and find the damaged area.

Sonoautomated

* Last updated by: sonoautomated on 9/26/2009 @ 9:25 PM *

新对话如下：

Thanks for the information Sonoautomated, I'll look into replacing the cable and picking up some deterrent.

Regards

新对话如下：

1500 feet of wire in the tree canopy is a great antenna for picking up surges from nearby lightning strikes, do you have any lightning suppression?

An inexpensive CAT-5 cable tester like the Fluke MicroScanner ($400 at Buy.Com) with an appropriate adapter will give you a guess at what's wrong with your cable, and how far away from each end the {break,short} is located. While you might not be able to find the velocity of propagation of your exact cable, testing from either end (*) will give you a ratio of lengths...

(*) If there's only one {break,short}

Radio wouldn't work?

I just confirmed that even though Ethernet cables are a maximum of 100M (300ft) in length, the MicroScanner2 will measure length to 1500 feet.

* Last updated by: wpns on 9/28/2009 @ 7:54 AM *

新对话如下：

Thanks for the feedback. The CR1000 is down in a hole and I was not able to get reliable RF communication with a Yagi or Omni at ten feet up, so went with the MD485. After talking with the project manager we decided to give the RF another chance. The idea would be to mount the antenna (either Yagi or Omni) up quite a ways, maybe 40 or 50 feet to see if we can get out. We have 12 CR1000's in the area which are all using radio's so the chances would be good with the antenna higher up we would have some success.

I don't have surge supression on the MD485's but do on the radios.

Thank you

新对话如下：

After doing a basic check on the cable (twist then A/B pair together and check the loop resistance) also check for ground referencing problems.

Then I'd recommend you try either spare MD485s or bring the pair together as, depending on the age of the device, they can degrade due to transient damage if not fitted with external protection. That damage can cause problems of intermitency, i.e. they may not just stop working.

新对话如下：

Thanks Andrew for the comments, I'll test the cable as you suggest.
Regards

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