Problem implementing watchdog using charge pump and InstruNet

[jack1]

I am using InstruNet DAQ INET 100 and INET 200 (customers spec) for a closed loop control application but having a problem implementing a watchdog that needs to be present in case the software or computer crashes.

Basically a 10Hz square wave is output to one of the INet 100 digital channels which is monitored by a charge pump circuit. If the 10Hz signal ceases then the charge pump trips the hardware control circuits disabling the stepper motors, pumps etc. This is required because if the software or PC crashed the INet units would continue outputting the last command they recieved.

The problem is that the timed loop I am using to output the high/low signal seems to create unpredictable response from the other INet hardware channels. All of the timer channels have been used of the INet 200 unit and in any event once set they just 'free run' until reset by software.

Does anyone have any suggestions for a better method of fail safe?

Thanks  John

[Mohamed H]

Hello,

Can you describe me the functionning of your InstruNet DAQ INET 100 and 200 because I do not know these devices. Do you use NI devices with your DAQ INET 100 & 200?

I suppose you are using LV 8.20 and I want to know from what you generated the 10 Hz square wave and what do you mean by unpredictable response from the other INet hardware channels?

Thank you.

[jack1]

Hi Mohamed

The INet units are made by a company in the USA called Instrunet. Basically the INet 100 is a remote self contained logging unit and the INet 200 a PCI card (www.instrunet.com).

In this instance they have been used at my customers request and no NI DAQ equipment is present in the application.

The problem of the monitor was resolved in the end by using a loop with registers and a time delay that simply toggled one of the INet 100 digital channels from Logic 0 to Logic 1 and by careful redesign of the main program . The actual output frequency was about 10Hz but could vary depending upon the particular routine that the main program was undertaking at that time. Precise frequency being un-important.

All of the time that the main program is running this 10Hz signal is output via the digital channel. If the PC or program should fail for any reason the 10Hz signal is lost and the circuit that monitors it flags a fail mode disabling all of the external hardware that is being controlled such as fuel pumps, positional stepper motors etc. If this feature was not present the INet units would retain the last command they were given and just carry on, which could prove a disaster as the Labview program operates all of the equipment in closed loop.

To be honest the INet units were a real pain to use and I have managed to convince my customer for future equipment to have NI DAQ fitted.

Cheers

John

[Mohamed H]

Hi John,

I understand the problem and thank you for having describe me the problem but in fact, it is a problem related to non NI hardware. I can help you if you are using NI devices and only if the INET manufacturer provide you files (dll) and documentationrelated to the functionning of the device and to control easily your harware because LabVIEW can do that using DLL files.

Thanks a lot.