how to use an external open/closed switch for event trigger

[JimN]

I use field point fp1000 with a thermocouple module 120. I am acquiring data from a thermocouple and wish to start the acquiring with an external trigger. The equipment now has a micro switch that needs to be wired to start the acquisition.

Any help on how to use the field point system to send this signal through the serial buss to accomplish this. It is a one time trigger that simply starts the sequence.

[Aaron_G]

Jim,

To start with, an FP-1000 and FP-TC-120 by themselves will not acquire/log data. The FP-TC-120 module is constantly running its A/D converter and placing the data into shared memory following it's configuration by the FP-1000 (starting roughly 1 second after the FP-1000 powered on). The FP-1000 is a poll driven network module. Thus, a computer (or other controlling device with serial port) needs to send a command to the FP-1000 to cause the FP-1000 to read the shared memory on the FP-TC-120. Thus, the reading of the switch and starting of the acquisition should be handled in the software, not directly in the FieldPoint hardware.

If you are wondering how to wire the FP-1000 and FP-TC-120 in order the make the switch readable by the FieldPoint system, there are several ways to accompish this. The easiest may be to add either a FP-DI-3XX module or a FP-CTR-50X module to detect switch closures. Alternatively, if the switch is a momentary normally closed type switch, you could place the switch in between one of the thermocouples and the terminal base to cause a temporary open thermocouple condition. Then, in software, you should continously monitor the channel that has the switch and watch the data quality. When the data quality indicates that the channel is in Open Thermocouple mode, you can start your main acquisition. There are two drawbacks with this method, since the FP-TC-120 module has an all channel update rate of 1.13 seconds, you will need to depress the button for at least 1.13 seconds. Also, you are introducing an additional cold-junction into the circuit that will not be compensated for which will decrease the accuracy of the one channel that has the switch wired to it. As a variant of this approach, if you are not using all 8 thermocouple channels, you can wire the switch between the In+ and In- terminals of an unused channel and scan that channel for Open Thermocouple (NC type switch) or Good Data (NO type switch) to figure out when the switch was depressed and when you can start acquiring data.

Regards,
Aaron

[JimN]

Thanks for the reply, I should state that I'm a rookie with a capital R.

The program I have, is written so that the FP-TC-120 data is read continously (after an input on the computer). I am looking at the data read on the screen, after that happens I need a trigger that starts a timed acquire/log sequence in the software. The problem is that the trigger is a microswitch on the machine.

To rephrase, I am looking at a continous feed on the computer screen. I need an external input from the machine (microswitch) read into the software to start the timing phase.

Would either of the two modules you mentioned (FP-DI-3XX or FP-CTR-50X) take care of something like this?

Jim

[JimN]

Thanks for the reply, I should state that I'm a rookie with a capital R.

The program I have, is written so that the FP-TC-120 data is read continously (after an input on the computer). I am looking at the data read on the screen, after that happens I need a trigger that starts a timed acquire/log sequence in the software. The problem is that the trigger is a microswitch on the machine.

To rephrase, I am looking at a continous feed on the computer screen. I need an external input from the machine (microswitch) read into the software to start the timing phase.

Would either of the two modules you mentioned (FP-DI-3XX or FP-CTR-50X) take care of something like this?

Jim