High Precision Handheld Signal Generator (FIT0778)

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This is a signal generator, yet the description/specs don’t tell you the frequency range it puts out. Look like the description is complete jibberish, goodness knows what it does.

Hi Peter
I think this is a specialist piece of kit.
Looking at the handbook (which is the usual translation from Chinese) it does not appear to have adjustable frequency as we know a “Signal Generator” to have. 4 - 20mA loop signals come into it somewhere, % which could be duty cycle, 50Hz is mentioned as is 1500 but no indication of what that is. The diagrams show connection to a PLC which could mean setting a signal or receiving a signal from it.
The text seems to be a copy of the manufacturers splurge but to find out you would have to find someone who has used one of these.

In a nutshell it doesn’t seem to be a “signal Generator” as the majority of people would associate that term with, but if it “generates” a signal of sorts the term would be correct. The fact it seems to be a special use device would be irrelevant.

Very puzzling
Cheers Bob

It’s a device for generating either a voltage or a current signal (such as used in field instrumentation). There is a information available about this device from various sources. For instance:
UCTRONICS Voltage and Current signal generator - YouTube
#779 Process Calibrator - YouTube

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Hi Jeff,

Thanks for sharing those videos, they are a lot more helpful than the manufacturer’s documentation. I’ll have them added to our product page shortly.

Hi Bob,

I have to agree it’s a bit confusing as I’ve almost never come into contact with a signal generator that wasn’t an arbitrary waveform signal generator.
Jeff’s linked videos give a great breakdown of why this device exists and how to use it so it’s good to know it does have it’s own little niche.

Hi All

Yes they do throw a bit more light on things. One thing though, both say the 24V input is to power that generator externally. Apparently not so, the handbook says that is a passive mode and not unlike a variable resistor. Most PLCs have a “high” or “on” input of 24V and this is to control the current into those inputs so is described as a “variable resistor” mode.
The videos did not get that far but there is a mention of 50Hz and % which i assume is duty cycle for I suppose is to check servo motors and 1500 which could be Hz (???) which coupled with % could control brushed motors or dimmers etc.

The videos do describe this device as more of a “calibrator” which is probably a better description.

One thing I did thing was a bit clever was calibrating this instrument with a couple of $35 DMMs. A bit of a joke I thought when they are adjusting the odd milliVolt and a few microAmps. At least the first one used a Fluke but even so the calibration status would probably be unknown.
Cheers Bob

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Hi Bob,

I thought that too at first but re-reading the manual I think perhaps it’s simply PWM dimming the display brightness of the unit.
I’ll make a note to have one unboxed and tested with our oscilloscope here so we can detemine what F0003 Display Mode in the table is actually referring to.

Agreed, it’s certainly not calibration by any industrial standard, but it’s nice to have the option to calibrate it in the event you do have a calibrated machine to improve the default calibration with.

Hi Trent

Interesting to see what you find

You can say that again.

It is if you have that option.
Fluke used to have an instrument called funnily enough a “Fluke Calibrator” which I think was a portable device. There used to be companies specialising in this and had vans (suitably air-conditioned at 25ºC) running around offering their cal services to others who needed a cal certificate. When I was working AWA had their own certified standards lab so looked after their own but this service was useful for those that didn’t.
Even so these instruments had to be checked themselves periodically.
Cheers Bob

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Hi Bob,

I very nearly began an apprenticeship in instrument calibration after doing work experience for a company that was doing calibration certifications for the aircraft industry. Most of the work was calibrating digital multimeters for Qantas. I couldn’t believe at the time what a set of calibrated weights cost.
At the time there were less than a dozen tradespeople with that specific job role left in NSW. I didn’t know people ran an equivalent service out of an air conditioned van as a mobile setup!

Hi Trent

That was 30 years ago. Don’t know about the present time but I suppose it makes sense. Far cheaper than doing your own and maintaining a certified lab.GEC Marconi also did their own cal certification at that time.
AWA used the lab as a test equipment repair facility as well as other tasks. They had a 1MHz and 10MHz Rubidium frequency standard signal piped throughout the factory for general use by anybody who had the need.
Cheers Bob

Certainly adding Voltage and Current to “signal generator” helps, although I would have called it a Voltage and Current source.

Although, as you say it seems to have some kind of PWM too, maybe?

Thanks for the responses everyone!

OK I read the manual :slight_smile: see https://raw.githubusercontent.com/May-DFRobot/DFRobot/master/FIT0778%20manual-EN.pdf

From my reading the percentage is simply a % of the voltage or current on the display:

"F003 Display Mode 0:Real Voltage 1:Percentage 0-100.0% 2:50HZ 3:1500 "

50Hz and 1500 as a display mode??? goodness knows AC? - hopefully @Trent5487676 will be able to shed some light :slight_smile:

Not my suggestion. For this type of signal the only thing that needs to be generated is a voltage (0 to +10v, 0 to -10V) or current (0 to 20mA). This will be read at the receiving end to confirm the connection is within spec. The ‘other’ part of the signal is ground, which is available without a generator.

It’s a demonstration of how to do the calibration - there is no suggestion that the calibration is to any particular standard. In fact, he points out that the DMMs were selected because the colours made them a nice pair.

Hi Jeff

I believe you are correct here. This statement jogged the old memory bank. This device specifically points to PLC connection. I seem to remember all the PLCs I have had dealings with accept a 0 - 10V analog input for a result (internally) of 0 - 500. or sometimes 4-20mA loop which also gets a mention in the instruction.

I will accept that but the point I make is that it is a bit misleading. It is there for anyone of any expertise level to digest. Would have been better if mention of this had been made in the video (both videos). In fact if this device is any good it could probably be used to do a quick check of the DMMs. Note I say “quick check” not Calibration…

I think the general feeling and answer to the original question is that this “generator” is mainly to provide appropriate “signals” for testing systems in an industrial control environment.
Cheers Bob

Hi Peter,

I’ve had a play around with the unit we have in stock in the warehouse and as you might have been able to tell from the videos navigating the configuration menu requires some seriously arcane instructions to be followed perfectly.
I haven’t been able to determine what the Display Mode setting does, but given how much fiddling it takes to adjust the setting I don’t think it represents a useful alternative application for the device.

I can see this device being useful if you just needed a pocket sized tool to give a reference current and reference voltage. You could set it up once to the outputs you need to test often then it’s a single button press to swap between your current source mode and voltage source mode. Any other settings on the device, between adjusting the reference current/voltage up or down is too much trouble.

This is certainly not a replacement for a arbitrary waveform signal generator, it’s a relatively simple unit, but what it does, it does very quickly and easily.