Function Generator question: What is GATE function?

[Cifrocco]

I just bought a new GFG-8255A Function Generator by GW Instek. Nice instrument, very lousy manual!!

I don't see any explanation of what the GATE switch is suppsoed to do. The display has the "GATE" indicator flashing quickly all the time, on every frequency range setting above the ones, that is, the tens, the hundreds, the thousands, etc. Nothing I do makes it stop blinking.

Can anyone shed some light on what this is for? Thanks.

 

[David Bridgen]

The "Gate" facility allows you to switch on a generator's output for the period of an externally applied "gate" pulse. Between pulses there is no output.

It should have a BNC socket somewhere for this purpose.

I looked at many web sites after Googling for the model number. Strangely, none of them, not even Instek, mentioned it. One did mention a "Burst" facility however, and this is (should be) the same thing.

 

[Roff]

The gate time on a counter indicates the time period (generated by the internal reference clock) used for counting, e.g., if the gate time is 0.01 second, and 1MHz is applied, 10,000 cycles will accumulate during the gate time. This means that the resolution is 100Hz. The decimal location is shifted over two places in order to show 1MHz. If you change the gate time to 1 second, the resolution will be 1Hz, but your counter will only update once per second. Looking at **broken link removed**, it appears that low frequencies are measured by counting the internal clock, gating it with the input signal (i.e., measuring the input period), and taking the reciprocal. This is the only way I can understand how they get 100nHz resolution on a 1Hz signal.
You will find links to the datasheet and the user manual on this page also. The user manual has some discussion of gate time, but never seems to define it.

 

[David Bridgen]

Hi Ron,

That's true, but on one of the sites I looked at there is a larger photo of the instrument and it has a "Gate" button. My assumption is that it would be used to select the gate function I described and with which you must be familiar.

Cifrocco's comment about the manual is quite warranted - I looked at the online one.

 

[Roff]

Hi Ron,

That's true, but on one of the sites I looked at there is a larger photo of the instrument and it has a "Gate" button. My assumption is that it would be used to select the gate function I described and with which you must be familiar.

Cifrocco's comment about the manual is quite warranted - I looked at the online one.

Hi David,
From **broken link removed**,

2a. Gate Time
Selector
Press this key to change gate time when use external
counter mode. The change order is according to 0.01s,
0.1s, 1s,10s cycle by pressing these keys.

I agree that the manuals basically suck.

 

[David Bridgen]

Whoops. I missed that Ron.

 

[Cifrocco]

Thanks for the replies, guys. I forgot that the GFG-8255A also has a built-in frequency counter, with the input BNC in the rear. I'm still not clear on what the GATE function is supposed to do. The pushbutton in the front of the unit, labelled "GATE" is a momentary pushbutton. When I press it, the green LED just above it will light, but as soon as I release the button the LED goes off, none of this affecting the flashing text "GATE" on the display. As you can see I have very little experience with such instruments, despite being in love with electronics since my infancy. I couldn't afford any serious test equipment until now .

I'll have to hook up the counter to a signal I can measure, then ponder once again on the descriptions given by you guys, and try again to gain some insight from the manual. The manual is very, very poor. There is no description of the GCV output BNC on the rear, for example. The grammar of the little bit of text they offer is so bad I think it would have been better to get the Chinese manual, it would be less effort to learn Chinese then read it, than to agonize through that English.

Oh well. Like I said at the outset, it's a solid instrument and seems to perform admirably given its price.

 

[David Bridgen]

Isn't that an input for a voltage to control the frequency?

 

[Roff]

There is no description of the GCV output BNC on the rear, for example.

From the user manual:

23. GCV Output
This is DC voltage output and its voltage amount will follow the change of Frequency.

I think this is what you trigger your scope on to synchronize it to the sweep. The datasheet implies this, in Chinglish.