How Often Should I Autotune?

[jvtruebl]

Hello,

I'm working with a Varian 450GC/220MS. Lately, it seems like after every run I need to re-adjust the cal pressure. Then, when I do that, it naturally wants me to autotune. At this point, I'm pretty much doing it after every run, and as a result (i think?) my precision has gone horrible. I can't get simple samples to have the same response two times in a row, because I'm adjusting the whole system between each run.

One of the errors that comes up every now and then, before autotuning, is Gate on Voltage Error. I've googled it and found nothing.

What's the deal?

[Hornet]

Hello,

I'm working with a Varian 450GC/220MS. Lately, it seems like after every run I need to re-adjust the cal pressure. Then, when I do that, it naturally wants me to autotune. At this point, I'm pretty much doing it after every run, and as a result (i think?) my precision has gone horrible. I can't get simple samples to have the same response two times in a row, because I'm adjusting the whole system between each run.

One of the errors that comes up every now and then, before autotuning, is Gate on Voltage Error. I've googled it and found nothing.

What's the deal?

What is your Electron Multiplier voltage?

[jvtruebl]

Hi David,

It says -1877 volts.

Came in today, had to autotune again. What's weird is, I always check the cal gas, and it looks fine. Then when I go to acquisition mode, the error comes up. Then I autotune it. On the first autotune, it fails. Upon failure, I look back at the cal gas and suddenly it isn't at acceptable levels. I adjust it, go back to autotune, and it works. I don't understand this cycle or why it happens pretty much after every 3 or 4 runs.

[Hornet]

When it fails the first autotune what does the log say? Some error about the Integrator Zero? Also...are you sure about that voltage? When multipliers are new they start from around 1500 volts and they will need to be at higher voltage when they get old, up to 3000 volts.

[jvtruebl]

The first time it fails it says "Electron Multiplier: Final Gain setting is incomplete (EM Voltage: 1750) The Final Gain cannot be set due to poor peak resolution (i.e. broad mass peaks) possible reasons include:
a) too many ions in the trap
b) Axial modulation too high or low
c) column flow too high or low
d) Cal Gas pressure too high


I don't think it's a-c because I bakeout the trap regularly, axial mod looks fine, and column flow is normal. Plus, whenever this error comes up, I go readjust the cal gas and then it's able to autotune. The thing is, this happens once every 3-4 runs, which doesn't seem like it should be required.

I'm checking the multiplier voltage right now and it says the following: "Multiplier Voltage: -1832V"

So right now, the cal gas is fine, and the system has been auto tuned, but still anytime I go into manual control, and then back into acquisition the following error comes up: "Module Hardware Problems are Present. Please Check log for details. Module 200-MS.41: Gate On Voltage Error."

I have no idea what that means.

[Hornet]

Manually adjust your EM voltage to 1750 volts and then regulate the cal gas pressure accordingly, it must stay from half to three quarters of the bar.
Then try a tune and report how it works.

Your calgas pressure was probably too high and the tune took EM voltage to that weird voltage, this is the only thing that comes up my mind with these info.
Try the procedure written above and report the results.

EDIT: i remember now that on your instrument the cal gas check uses the EM voltage calculated from the last tune and not the manually written one.
If this is the case your only possibility is to gradually decrease the cal gas pressure to an acceptable level and then tune again.