ITech IT6121 precision power supply always display a tiny reading

[jjloki]

 


Hi everyone,

I hope you're all doing well. I've recently encountered a puzzling issue with my ITech IT6121 Precision Power Supply, and I'm seeking some guidance from the knowledgeable community here at EEVblog.

The problem I'm experiencing is that regardless of whether I turn on the output or not, the measurement meter consistently displays a tiny output reading. It's a cause for concern because I'm unsure whether this is normal behavior for the equipment or if there's an underlying issue that needs addressing.

I've tried troubleshooting on my own, including checking the connections, reviewing the manual for any relevant information, and experimenting with different settings, but unfortunately, I haven't been able to resolve the issue.

If you have any insights, advice, or troubleshooting steps that you think might be helpful, I would greatly appreciate your input. Additionally, if there are any specific tests or checks you recommend conducting to diagnose the problem more accurately, please let me know.

Thank you in advance for your assistance. I'm looking forward to hearing from you and hopefully getting this issue resolved soon.

[alm]

1 mV output when set to 0.0000V does not sound concerning to me. What is the specification for programming voltage accuracy? Does the offset remain when you set it to a higher output voltage? If this is out of spec, then my guess is that's an adjustment issue.

[jjloki]

1 mV output when set to 0.0000V does not sound concerning to me. What is the specification for programming voltage accuracy? Does the offset remain when you set it to a higher output voltage? If this is out of spec, then my guess is that's an adjustment issue.

Thanks for the reply alm.

Sorry for the confusion and I should have decribed the issue more clearly. If you look at the picture I just attached, even if I turn off the output. There is a small reading 0.001V (now it's 0.002V) displayed by the internal voltage meter and 0.00015A (now it's 0.00030A) displayed by the current meter. That's two reading's will stay there if I turn on the output (eg. set 1V, it display 1.001V etc)

Anyway to get rid of this?

Thanks!

[alm]

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?

[J-R]

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.

[jjloki]

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?

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]

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.

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]

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.

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.

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]

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.

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.