Magnetic Pickup


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First let me say that I am new to UE9 so please make answers simple (not like Users Guide which is way over my head)

I'm using DaqFactory and all I want to do is read the frequency from the magnetic pickup on my turbine flowmeter. The frequency will vary between 100Hz and 1500Hz and the voltage is about 20-60 mV.

I connect to the UE9 by ethernet and can read analogue input OK.

I have configured the Labjack as Device #2 as I have other devices as 0 and 1

I have connected my pickup to FIO2 and used quick device configuration to set up 1 timer and 1 counter

which I assume will occupy FIO0 and FIO1 respectively. Although I have no idea what I'm going to do with these.

The timer clockconfig is 750khz, but I don't know what the divisor is for so have not set it.

Mode ? - I have no idea what PWM or quadrature are so I chose falling edge input

Value ? -

Where do I go from here - it seems very complicated

I looked at the UE9-CounterModes_Simple example but there seems to be a lot of script, is this just doing the same as QuickConfiguration. I really dont understand the logical process and which bits i need.

Help gratefully recieved

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Two things to get started, before we get into DAQFactory stuff:

1) Decide if you want to use a Counter or Timer (or both), and let us know. Check out the following topic:

2) So you get a square wave from your sensor, where the low state is about 20 mV and the high state is about 60 mV? That will not work with the digital (counter/timer) inputs. Looking at the digital logic levels specified in Appendix A of the UE9 User's Guide, you want a low of -0.3 to 1.0 volts, and a high of 2.3 to 5.3 volts.

One option would be to use some sort of hardware to condition your signal to the proper levels. Perhaps the sensor manufacturer has suggestions for interfacing to standard digital logic?

The other option would be to use an analog input, rather than a timer or counter. You could collect the data real fast, and then use software to analyze the waveform and figure out the frequency.

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I suppose I expected to use a counter as my flowmeter has a K factor of 273 pulses per litre.

I dont have a square waveform. Magnetic pickups give a sinusoidal waveform.

If I have to go to the expense of buying signal conditioners, I might as well buy a frequency to voltage one and ditch the Labjack.

I was persueded to buy the labjack as a digital interface because my 32 channels of smart A/D cards don't accept digital signals.

The write up on the labjack makes it seem like it is very flexible, but in fact it is so complex to implement that I for one will be consigning it to the shelf, until someone produces a user friendly manual.

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Even if you have a frequency to voltage converter, you still need the UE9 to get the voltage into your computer. In addition, a typical frequency to voltage converter works with logic level signals, which you do not have, and thus would not do anything anyway. For instance, the following standard 5B module would not work with your signal:

The problem is that you do not have a logic level signal. The UE9 counters/timers, like most counters/timers, work with standard logic level signals. Here are some options I see:

1) Check with manufacturer of the sensor, to see how the signal is typically handled. Maybe they have different sensors with easily handled outputs such as driven TTL or open-collector. Or maybe they have a good suggestion for converting the signal to logic levels.

2) Build your own signal conditioning using a comparator where you set the threshold to 40 mV.

3) Handle the signal in software using an analog input. This is more complex in software, but requires no special hardware. You would stream the analog input signal at say 20 kHz. Then, you process a block of data once per second, counting transitions through a threshold to determine the frequency. If you choose this route, we or Azeotech can help further and perhaps make an example for you.

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