SteveL

My previous post concerning thermistors resulted in my sending a thermistor to NI (UK). The engineer wanted to have a go at making it work with a USB-6008. He is still working on the problem. In the mean time I need to get an experiment working for our undergraduates to play with in 4 weeks time. I thought I'd try the LM35 because it needs only a 5V supply to work. Sure enough; I had it woking within 5 min's and was getting a reading (10mV/degree C) on my multimeter. OK I thought, connect it to an input on the 6008 and use LV express to create an RSE input: simple! NO! it gave a constant 3.3mV out, no matter what the temperature. So I disconected it from the DAQ and it worked again. Try it on a different input; same result. Check NI developer forum and discover that it is a known problem with several users. I read all of the messages that had been sent and found one from NI that suggested 2 things. The first one didn't work and the second one tried to explain how to wire it but didn't give a circuit diagram. Unless anyone has had any experience using the LM35DZ with the 6008 I will have to abandon the temperature experiment. Anyway, I am going to try and get an electret microphone to work with the 6008 today: I really hope this works (-: Steve Lawson P.S although the 6008's were cheap (we bought 30) I am begining to wonder if it would have been cheaper in the long run to go for a better unit.

Labview 8.0 connected to a USB-6008 I am using 'BC Components' NTC Thermistor. I used the express VI to create a Vex input and entered the A,B,& C values from the datasheet. The thermistor is the 10K version and I placed a 10K resistor in series with it. I wired as though it were a 3 wire device, as is shown in the connection diagram, and applied 2.5 volts (generated by the same USB-6008) to it. (I also tried a seperate power supply) I get completly the wrong temperature readings out of it! I called the NI help line in the UK and the engineer confirmed that I had done everything correctly, but couldn't understand why it didn't work. Any thoughts? Steve Lawson

OK, I just answered my own question: The solution was simple. I took the message box outside the case structure. Now, this on it's own doesn't fix the problem but I also added a compound 3 input AND gate. The inputs to this were from Limit Switch 1, the On/Off switch, and the switch that reverses the motor direction (sorry, I didn't mention that last one). I then added more code that changes the Forward/Reverse front panel switch to the opposite of where it was. Now, these inputs will only give an output when a/ the motor has stopped, b/ the Forward/Reverse switch is in the correct direction for that Limit switch, and b/ that Limit Swtch has been activated. All of this is only TRUE when the CASE structure has already done it's bit and finished. Therefore the message box doesn't interfere with anything. Steve. Thanks to everyone that answered: I composed my solution reply and sent it before I realized that you had all taken the trouble to answer, sorry. Now, I did try putting a sequence inside the case statement but it isisted on the last sequence (the message one) being finished before it would do what was in the first two boxes in the sequence. I checked the NI site and there was an article there that said something about all things being completed in a sequence before it would carry out the instructions in the whole thing? I thought this was odd! Until 2 weeks ago I had never used Labview (I was brought up on BASIC ,VB, and Delphi). Programing with pictures has been a struggle but I'm getting the hang of it. Right, I must read about threads and state machines :-) I am sure that in a few months time I will look back at this first program and wonder how I managed to write it so badly: That's programming. I am also sure I will be asking some more questions, and this time I'll check for answers before sending my own replies! Have a good weekend. Steve Lawson York University Physics Department.

I am relativley new to Labview and I'm having a problem with a message box in LV8. The task seemed simple: LV is controlling a relay that starts a motor. There is a front panel switch that starts & stops the motor. The motor moves a small metal table from left to right or right to left. There is a limit switch at each end of the table traverse. If the user attempts to drive the table too far in either direction it will trigger a limit switch. The program monitors the switches and if either one is activated it switches off the power to the motor. All of that bit is working. Then I thought it would be sensible to tell the user that it had happened, and which switch had been hit. A message box, I thought! Well, no, not that easy. To keep things simple I decided to use two CASE structures: one for each switch. ( I am sure there is a much better way but I am still learning). Each CASE structure has a Property Node of the Front Panel motor on/off switch within it that turns the motor off. If I put a message box within either structure, the program ignores the On/Off Property node until the user clicks OK on the message. This means that the motor continues to run! Any help would be appreciated. Steve Lawson.