How to reconnect cFP-1804 to network

[RavensFan]

Centerbolt,

How do you set up the logic for the One-Shot mode?

I'm thinking the off delay is what the poster would want with this logic:

1.  Set the timer for the maximum amount of time that is acceptable for the heaters to be on in an uncontrolled state.

2.  Monitor the the status of the network.

3.  If the network status is OK, flip the digital output on then off to the trigger of the timer so it resets.  Do this more frequently then the Off -Delay of the timer defined in #1.

If the network goes down, the DO is not toggled on then off.  The timer will run out after the time set in #1 killing power to the coil of the relay that is the true Heater on/off controller.

One day I may need to do something like this, so I'm interested in how to apply the logic to some of the other control modes of these timers.

Message Edited by Ravens Fan on 12-19-2007 04:15 PM

[Wayne.C]

Ravens Fan,

You make a good point.  One-shot mode and Off Delay will work roughly the same with one minor difference.  In One-Shot mode the timer starts when the trigger signal 'S' is applied to the relay.  If the relay is not retriggered before the end of 'T', then the output will shut off. 

In Off Delay mode, the timer starts when the trigger signal 'S' goes away.  I guess you could look at it as rising edge vs falling edge.  Here is a link timing diagrams for this relay.  http://magnecraft.thomasnet.com/Asset/Stránky-z-Section-5_3-2.pdf

Probably does not matter which one you use.  I'm probably just partial to One-Shot because it's a function I've implemented a lot in the past with 555 timers.

[RavensFan]

Thanks,

That makes sense.  Particularly the comment about trailing edge vs. leading edge.  I had looked at one of the specs. at the website you had linked to previously  (this link) and I had a hard time decoding what they were saying.  The time t mixed in the hatch marks and the scrambling of S, R, and U didn't help.  Your last link definitely gave me a clearer picture as to what each type does.

[Wayne.C]

Ravens Fan,

I've had some time to sleep on this an realized there is one other very important difference between the two modes.  If you use the Off Delay and your trigger output from cFP hangs high, relay will never time out and can't provide watchdog protection.  That's because the Off Delay mode is level triggered.

The One Shot mode specifically says that the trigger signal must go low and then high again to reset the timer.  That means the One Shot mode has a edge trigger and should protect no matter what state the trigger output is in when network is lost.

[RavensFan]

That's a good point.  While it is highly unlikely the fieldpoint would freeze up in the short interval time while the DO pulses high, it is still a possibility and one I wouldn't want to risk, especially for on equipment where the user has deemed it necessary that something extra is needed in terms of safety.  I agree with you that the One shot retriggerable is the better choice over the off delay.

[AnalogKid2DigitalMan]

I agree, I did not consider the odds of a high latch during the reset input pulse. Retrig one shot is the fail safe route to go.

-AK2DM

[Wayne.C]

Mellobuck,

You initial post gets 5 stars simply because ( Quoting the AnalogKid's signature 😞

~~~~~~~~~~~~~~~~~~~~~~~~~~
‘It’s the questions that drive us.”
~~~~~~~~~~~~~~~~~~~~~~~~~~

[AnalogKid2DigitalMan]

You can thank Trinity's line from "The Matrix" for my signature, seemed fitting for this Forum

[Mr._Jim]

Hi folks,

It looks like I'm waking a dead thread, perhaps with some risk, but I'm seeing the exact same behavior on my fairly new cFP-1804.  That is to say that, when I disconnect the Ethernet cable for more than 5 seconds or so, the link lights turns off and the device becomes unresponsive.  We're using this cFP model in a few of our products, and the possibility of communication failure at a remote site makes me rather nervous.

There was a lengthy discussion on watchdog timers, but I'm wondering if the problem on the cFP device itself was ever resolved? Is there any known workaround within the scope of the cFP-1804?  Has any new firmware been released?

I've tried the following:

1. Unchecking the "Halt system if TCP/IP fails" checkbox in MAX

2. Verifying that the "WatchdogTimeout" variable is set to zero in the Distributed System Manager

Has anyone figured out a way around the Ethernet issue?

Thanks in advance,

Jim

[DiscoBall]

Hi Mr. Jim,

Did you check to ensure that the Network Watchdog Configuration in MAX was set to Disabled? See the picture below for its location. Also, these may or may not be helpful:

KnowledgeBase 17F9KN8U FieldPoint Watchdog Timer Questions

NI Developer Zone: FieldPoint Watchdog Timer

NI Developer Zone: Guarding Against Network Failures: How to Configure the Network Watchdog Timer fo... (this is an older document using FieldPoint Explorer, but relavent).

Message Edited by DiscoBall on 03-05-2009 09:00 AM