EEVblog Electronics Community Forum
Products => Test Equipment => Topic started by: Tony_G on April 08, 2017, 07:53:22 pm
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Hi All,
Is there a trick to getting this set other than selecting the 10V or less ranges? I'm trying to track down a problem with a 3403C on its DC 10mV range.
The circuit tracks into a voltage divider that should halve the value (it's basically two ~9.5M ohm resistors) - I was checking the resistors and confirming voltages by unsoldering the divider and tracking the 10mV DC through.
With my DM3058 set to 10G input resistance, I see exactly what I expect, 10mV through the circuit to the unsoldered end of the ~9.5M resistor.
Setting the 2015THD to 100mV range should make the input resistance greater than 10G and yet when I get to the end of the resistor I'm actually seeing ~2.4mV (which actually implies my input resistance is somewhere in the range of 25M ohms).
Have I missed another option on the meter somewhere that can switch the input resistance?
Thanks,
TonyG
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AFAIK there's no trick, it's automatic.
Your meter might have excessive bias current. It was discussed in several topics how it can be measured and fixed (like here (https://www.eevblog.com/forum/beginners/o-qn-on-funny-nplc-multislopenoise/msg825826/#msg825826) and here (https://www.eevblog.com/forum/repair/keithley-2015-repair-and-the-input-buffer-replacement/), for example).
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There is no trick or switching impedance function on Keithley's (2000,2015,2001/2002, likely 2010 too). It should be 10+G on 0.1-1-10V ranges, unless meter is faulty. Make sure autoranging is disabled.
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Thanks z01z & TiN.
I'll take a look at the bias current and see if that was the issue (I did have the meter manual set to the range).
TonyG