Checking CMRR on a Yokagowa 700925 Differential Probe - Page 1
Forum section: electronics / testgear

author: watchmaker
author_rank: Unknown
timestamp: May 27, 2025, 11:41:17 pm
content: I bought this with some stuff last year and just made the mistake of watching Dave's videos on differential probes and how to evaluate them.Below is the Bode plot generated by SDS824x and SDG2122x. The screenshot is a little crowded but the CMRR at 1MHz is 42dB (from the list which is not scrolled to 1Mhz) and the spec sheet sez 35 dB.The probe is calibrated at 1KHz and I checked the BW which does not fall off until after 15MHz. I did find its amplitude for DC agrees with my DMM if I set the scope attenuation setting to 9.9. At 10x it clips at just over 50V, which is what I would expect since it is a 50/500 volt probe.Does this look like I did the Bode right?SDG Ch1 to T terminated with 50inline; other end of T BNC banana adapter (pos) to both probe leads. Input to Scope Ch 1.Probe output to Scope Input Ch 2 (datasheet sez output is 1M) so no in line terminator.If I make the phase curve visible, it does shift at around 15MHz, which is the rated BW of the probe.Are there settings I should use in the Bode Config to make things clearer?Thanks. Should be concentrating on RLC and differential calc; but....

author: tautech
author_rank: Super Contributor
timestamp: May 28, 2025, 12:07:51 am
content: Use the Print button on the front panel for other menus that show settings to remain visible.

author: mawyatt
author_rank: Super Contributor
timestamp: May 28, 2025, 12:18:39 am
content: Set BW on all DSO Channels to Full.Best

author: watchmaker
author_rank: Unknown
timestamp: May 28, 2025, 07:00:11 pm
content: I have the scope inputs set to full. I did one to 20 MHz and one to 5 MHz. The tables are listed separately.I forgot to wrap the leads so the results may be suspect.Yokagawa's CMRR specs are pretty simple: BTW, Yokogawa sez these values are typical but not guaranteed!60 Hz -86 dB20KHz -66 dB200KHz -56 dB1MHz -40 dBNoise is around 1.4mVrms. No spec for that.My interpretation is this probe is "ok", but not as good as a modern differential probe. Sqishy CMRR at low frequencies, and decent CMRR until about 3MHz. Is that a fair interpretation of the results?I will probably keep it because I do not expect to deal with more than 120 volts; no tube B+ supplies.Of course, I thought to test this after I purchased a DP702 from Saelig for $210; almost $100 less than the DP700. Both have the same specs except for BW so I figured WTH. Not sure I understand the pricing.https://www.saelig.com/miva/merchant.mvc?Screen=PROD&Store_Code=SOS&Product_Code=mdp702OOPS, can't upload csv files (data).Data list:Frequency(Hz),CH310,-68.5553774,128215.128,-55.0237917,256420.256,-50.2939014,384625.385,-52.3748165,512830.513,-48.0206367,641035.641,-47.6245486,769240.769,-47.9739311,897445.897,-47.0979368,1025651.03,-45.4770098,1153856.15,-43.6981696,1282061.28,-40.7721943,1410266.41,-42.8713281,1538471.54,-41.6199875,1666676.67,-42.6729085,1794881.79,-41.006862,1923086.92,-40.3766548,2051292.05,-38.1146651,2179497.18,-40.4435034,2307702.31,-39.0429655,2435907.44,-38.5815115,2564112.56,-39.2541931,2692317.69,-36.7892893,2820522.82,-39.2114985,2948727.95,-36.526438,3076933.08,-36.61743183205138.21,-36.04759493333343.33,-37.09570183461548.46,-35.37955023589753.59,-36.05008173717958.72,-36.38975753846163.85,-36.03519223974368.97,-35.39213614102574.1,-35.9636366,4230779.23,-34.96556174358984.36,-35.611306,4487189.49,-35.08795314615394.62,-35.59770234743599.74,-33.94882524871804.87,-34.94553945000010,-34.9617365,Thanks.