Products > Test Equipment

Bench LCR Meter Observation

<< < (2/2)

rf-messkopf:

--- Quote from: mawyatt on July 02, 2024, 11:55:50 pm ---We are not sure "how" these schemes are implemented tho, could be in hardware, or software, or a combination for both types, or not at all!!

--- End quote ---

In this video the designer of the old Hameg/R&S HM8012-2 explains the block diagram:




--- Quote from: mawyatt on July 02, 2024, 07:36:45 pm ---When we made low resistance Kelvin measurements with the IM3536 with Cable Compensation Off, the results exhibited the negative inductance (capacitance) as "seen" with the Tonghui TH2830 (no Cable Compensation available) when also using the same Kelvin Clips.

--- End quote ---

Have you experimented with a full open/short/load compensation, using a known impedance as a load (which may be difficult to realize)? It is my understanding that at least the R&S HM8118 also compensates for phase delay of cables when open/short/load compensation is used. I just checked the HM8118 manual as well as the manual for the newer LCX meters, however, they are silent on the actual math behind that compensation. No idea if that is equivalent to a full one-port compensation of a VNA with three known standards. I would have to make some experiments...

gamalot:
My NF ZM2372 has a cable length correction key which can be found on the front panel, so I don't have to RTFM.

It's just a rough compensation, choose one of the fixed lengths of 0/1/2/3/4 meters.

Sensorcat:

--- Quote from: mawyatt on July 02, 2024, 11:55:50 pm ---Don't think the actual complex Z is measured as magnitude and angle, but more the complex voltage directly across the DUT and the complex current directly thru the DUT.

--- End quote ---
Dpends how you define 'measurement'. The LCR meter measures complex Z in the same way a DMM 'measures' resistance. My intention when I wrote that it measures Z was to express that one should not think L, C, R are the primary parameters or that anything in the measurement part of the instrument is altered if you change the display parameters.


--- Quote from: mawyatt on July 02, 2024, 11:55:50 pm ---This scheme doesn't actually measure the DUT current but the result of the DUT current being "forced" thru a scaling transimpedance amplifier to "convert" the DUT current into a measured voltage which represents the current with appropriate scaling factor.

--- End quote ---
Like a thermocouple, which does not actually measure temperature, but voltage...


--- Quote from: mawyatt on July 02, 2024, 11:55:50 pm ---How the next part works to create the desired result is uncertain/questionable, at least for us.

--- End quote ---
There's no reason to speculate about that, or to regret that we cannot know, because the 'Impedance Measurement Handbook explains' it:

https://www.keysight.com/de/de/assets/7018-06840/application-notes/5950-3000.pdf

It's a relic from the times when HP told almost everything about the internals of their instruments. Nevertheless, Keysight still publishes this precious resource. I discovered it when I had to design my first signal conditioning circuit to interface a gas sensor that has a variable impedance. Long ago.

rf-messkopf:

--- Quote from: Sensorcat on July 03, 2024, 06:21:05 pm ---https://www.keysight.com/de/de/assets/7018-06840/application-notes/5950-3000.pdf

It's a relic from the times when HP told almost everything about the internals of their instruments. Nevertheless, Keysight still publishes this precious resource. I discovered it when I had to design my first signal conditioning circuit to interface a gas sensor that has a variable impedance. Long ago.

--- End quote ---

Thank you. That is a really good resource. It also confirms that a full open/short/load compensation will account for any linear circuit between terminals and measurement plane. At least if it is implemented properly in the firmware.

mawyatt:

--- Quote from: Sensorcat on July 03, 2024, 06:21:05 pm ---

--- Quote from: mawyatt on July 02, 2024, 11:55:50 pm ---How the next part works to create the desired result is uncertain/questionable, at least for us.

--- End quote ---
There's no reason to speculate about that, or to regret that we cannot know, because the 'Impedance Measurement Handbook explains' it:

https://www.keysight.com/de/de/assets/7018-06840/application-notes/5950-3000.pdf

It's a relic from the times when HP told almost everything about the internals of their instruments. Nevertheless, Keysight still publishes this precious resource. I discovered it when I had to design my first signal conditioning circuit to interface a gas sensor that has a variable impedance. Long ago.

--- End quote ---

Thanks, the Keysight Handbook does a good job of discussing the various methods. Wish KS would still publish details about their instruments as in the old HP days, but that's long gone now with the immediate bottom line mentality all OEMs march too :palm:

After reading it appears our Hioki IM3536 utilizes the more complex version of the Auto-Balance Bridge technique, and the Tonghui TH2830 may employ the simpler version. Some day we'll probably dive inside these meters to see whats going on!!

Best,

Navigation

[0] Message Index

[*] Previous page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod