1689 LCR Meter Specifications

[ElizatronicWarfare]

Hi all,

I have just come into possession of an old QuadTech 1689 RLC Digibridge (i.e. LCR meter), but the specs don't seem to line up with my expectations. Is it really twice as good as a HP/Keysight 4284A/E4980A (±0.02% vs ±0.05%)? Is there some specific operating condition required I am not aware of to reach these specs? Are HP/Keysight LCR meters really not that good? I do not have as much experience comparing LCR meters as I do operating them, so I appreciate any context you all can provide.

Regards,
ElizatronicWarfare

[rodpp]

Yes, the Genrad 1689 digibridge is a precision instrument, even used in calibration labs. IET Labs still sell it new for around USD 8-9K.

They have an online tool to calculate its accuracy:
https://www.ietlabs.com/notes/digibridge_accuracy_calculator

Read some available tech notes available here:
https://www.ietlabs.com/notes/Digibridge

This one is about metrology applications of the Digibridge, using the 1689:

https://www.ietlabs.com/pdf/application_notes/035005%20Digibridge%20for%20Metrology%20Applications.pdf

[rodpp]

This Keysight marketing material compares the E4980AL vs the Digibridge 1693:

https://www.keysight.com/us/en/assets/7018-03933/flyers/5991-2314.pdf

The 1693 is very similar to the 1689, but goes to 200KHz while the 1689 stops at 100KHz.

The accuracy graphics shows that above 10KHz the E4980AL is much better than the digibridge. But for low frequency (10Hz-10Kz) the digibridge is better.

Of course, as a Keysight marketing material it shows the specs in the more favourable way to Keysight equipment.

[rodpp]

One interesting thing about the 1689 is the calibration is performed using only a set of four known resistors of specific values: 95.3 kΩ, 5.97 kΩ, 374 Ω and 24.9 Ω. So, if you have a resistance decade box and means to measure these values with high precision (10ppm), you can "easily" calibrate the 1689.


IET Labs sells this set of resistors as a kit, NIST traceable, but expensive:

https://www.ietlabs.com/1689-9604-digibridge-calibration-kit.html

You probably will get more information regarding the 1689 digibridge asking in the Metrology section of the forum.

[zrq]

I adapted the Javascript code of the IET's 1689 and 1693 online accuracy calculator (https://www.ietlabs.com/notes/1693_digibridge_accuracy_calculator) for programmatic evaluation in python, and I plotted the calculated accuracy of the main parameter as a function of frequency and impedance to allow easy comparison with competing models. The SecondaryUnitValue (D/Q) is set to 0.

The accuracy specification of A/K E4980A is attached for reference. It seems 1689/1693 significantly outperforms competitors in the low |Z| region (<100 Ohm) but many other LCR bridges are better for higher |Z| (>10 KOhm). Of course, due to the ancientness of the ADC and DSP in 1689/1693, the frequency range is limited to <100kHz and 200kHz (only a single point) and the noise is likely worse than more modern LCR meters.

[croma641]

It seems that the 1692 is exactly the 1689 with different firmware. Simply replace it and redo the calibration


https://www.eserviceinfo.com/downloadsm/34470/Genrad%20Quadtech_1659%201689%201692%201689M.html