triangular waveform analog output

[prafullashahi]

Hello,

I want to send an analog output signal that changes with time:

-Increase from 0-10 V at a rate of (3.2/7 = 0.4571) V/sec

-Wait at 10V for 2000 ms

-Decrease from 10-0 V at a rate of (3.2/7 = 0.4571) V/sec

Which function would work best for this purpose?

I was trying to use the triangular waveform, but am not sure how to use it in a while loop because it isn't working as expected.

I have a Volt-time array which can simulate the signal...if only I knew how to use that to generate my waveform.

I'm using a Measurement Computing DAQ (USB 3103) with 16 bit resolution. Not sure if you need max sampling rate for analog output, it isn't there in the manual.

Thanks,

Prafulla.

[mikeporter]

As slow as the outout is changing I'm not sure you need a function. The voltage will ramp up for about 22 seconds, stay high for 2 seconds, then back down (another 22 seconds) and then be low for 2 seconds -- for a total cycle time of 48 seconds, give or take a bit.

A real simple state machine would handle the job fine. All you would need is 4 states:

* ramping up
* hold high
* ramping down
* hold low

A shift register would hold the last value. The output update rate would depend on the output resolution and how smooth you want the signal. In any case you should have a simple low-pass filter on the output to filter high freq noise from the output.

What will this signal be driving?

Mike...

[Dennis_Knutson]

Consider the Ramp Pattern to generate your waveform. This just generates an array. You can use array to ramp up, a constant array for the soak, and another to ramp down. Concatenate into a single array and use the DAQ device timing properties if it supports hardware timed analog output.

[prafullashahi]

@mikeporter

The signal will be sent to a controller controlling the pressure in a hydraulic system from 0 to 5000 psi. I'll send an analog signal to the controller and the controller will send a PWM output to the valve.

The response time of the hydraulic system is very high, if I change the pressure by a 1000 psi, the flow takes about 2-3 seconds to stabilize, doesn't affect my application much though, as I don't need to control the pressure to a specific value. It just needs to go up to 5000 psi and back to zero and measure pressure-flow at equal intervals of time. The max pressure shouldn't exceed the rating though, which is almost always within +/-25 range of 5000 psi.

Thanks

Prafulla.

[prafullashahi]

@mikeporter

I'm trying to get the ramp pattern using a state machine.

Should my state change (from Ramp up to Hold high) when 22 seconds have elapsed (time-driven) or when the ramp function has ended (event-driven)?

How should I do either of them? I don't know how to check when the function has ended or how to measure absolute time inside a while loop.

Could you please provide an example VI for the same?

Thanks,

Prafulla.