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ITech IT6121 precision power supply always display a tiny reading

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jjloki:

--- Quote from: alm on April 01, 2024, 04:02:29 pm ---What is the specified accuracy for voltage and current programming and read back? Do you have access to a DMM that's in calibration with a better uncertainty than the power supply?

--- End quote ---


I've attched the specs here. Basically the upper two rows that I circled out in red is for programming accuracy and the bottom two rows is for read back accuracy.

The very point that I was very confused about and unsure of is whether the meter should have a tiny reading even if the output is not turned on. I just assume it should display "0V 0A" as the "zero" point. No?

Also very unfortunately, I didn't find any useful information regarding the calibration process for this power supply.  :-\

jjloki:

--- Quote from: J-R on April 01, 2024, 06:25:23 pm ---It's doubtful the OP fully understands the concepts especially since they claimed to have already read the entire manual and are still thinking there is something wrong.

The short answer is that there is nothing wrong.

Per the specifications in the manual, the 12 month readback accuracy is:
Voltage ±0.02%+3mV
Current ±0.05%+2mA

So ignoring the percentage portion of the specification, at ANY TIME, the indicated display could be 3mV and 2mA away from the actual value and still be considered working correctly.

In the photo, it's only 1mV and 0.15mA off, which is great.
In your second post, you state it was 2mV and 0.3mA off which is still fine.

--- End quote ---

Thanks for your informative reply J-R. Really appreciate that!

I did tried to do some research and did find that the tiny reading is within the spec. However, I am not too sure whether the spec is also applicable to the "zero" point when the output is in off state. so just want to check with people who is more experienced with these. I also searched the user manual and unfortunately it talked nothing about that.

2N3055:

--- Quote from: jjloki on April 02, 2024, 05:12:46 am ---
--- Quote from: J-R on April 01, 2024, 06:25:23 pm ---It's doubtful the OP fully understands the concepts especially since they claimed to have already read the entire manual and are still thinking there is something wrong.

The short answer is that there is nothing wrong.

Per the specifications in the manual, the 12 month readback accuracy is:
Voltage ±0.02%+3mV
Current ±0.05%+2mA

So ignoring the percentage portion of the specification, at ANY TIME, the indicated display could be 3mV and 2mA away from the actual value and still be considered working correctly.

In the photo, it's only 1mV and 0.15mA off, which is great.
In your second post, you state it was 2mV and 0.3mA off which is still fine.

--- End quote ---

Thanks for your informative reply J-R. Really appreciate that!

I did tried to do some research and did find that the tiny reading is within the spec. However, I am not too sure whether the spec is also applicable to the "zero" point when the output is in off state. so just want to check with people who is more experienced with these. I also searched the user manual and unfortunately it talked nothing about that.

--- End quote ---

It is right there in the specifications:

Voltage ±0.02%+3mV  (±% of reading + offset).

Percentage is of read value (so ±0.02% of 1V, or  ±2mV) and offset is a constant, ±3mV applied to any value shown , including 0.
So for 1V it should be 1V±5mV (max error)  and for 0 V it should be 0V±3mV. (Yes it can be few mV negative)

Only if specification explicitly specifies accuracy at 0 point, than you will have that specified separately.

thm_w:
Part of the confusion here may be that most supplies choose to show 0.000V when the output is set to off, regardless of the actual output.

A good PSU will always display the voltage on the output, regardless of if the channel is on or off. IMO.
This way you can see if the channel is being backfed or if the output capacitors are taking a long time to decay.

jjloki:

--- Quote from: thm_w on April 03, 2024, 12:19:32 am ---Part of the confusion here may be that most supplies choose to show 0.000V when the output is set to off, regardless of the actual output.

A good PSU will always display the voltage on the output, regardless of if the channel is on or off. IMO.
This way you can see if the channel is being backfed or if the output capacitors are taking a long time to decay.

--- End quote ---

Yes, exactly. I thought being exactly "0" when the output is off is the "standard" behavior.

That's very good point. Thanks for your reply.

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