TIDA-010232: AMC3330DWER & ADS131M06IPBS

Thanks for the update ,we will check and update you further. 

We also have another Query regarding the Earth Loss Detection. In our circuit we have used two additional TPSI2140QDWQRQ1 (Switch) for adding a known resistance of 1.245 M ohm from DC+,DC- to earth.The RisoP ,RisoN equation will be now modified to Equation 21 & 22 (TIDA-010232). But what would be the accurate end result when earth is present and when its not present. Is there additional formula other then just calculating RisoP & RisoN (modified using Eq 21& 22). Also if you could provide any test example which help us understand the behavior under earth present and absent condition.

Hello Andreas ,

Thanks for explanation of the behavior under Earth Present and absent condition, we will test and update you further on that . 

Meanwhile, we are testing for isolation monitering in which we have used 2 switches only )

 we have calculated the RisoP & RisoN via the the method discussed before, and also used the modified equation you suggested for calculating VP ,VN

(Visolation =  VinADC* (RinAMC +Rst)/RinAMC *1/GainAMC)

We are following the software flow .

one thing we observed that VinADC was having fluctuation , also sometimes the value was going in negative ,which would eventually effect Visolation, and RisoP & RisoN values. Please find the Excel attached. Can you confirm if the values & formula are okay .

Regards isolation_check_pos.xlsx

Kanhaiya

As per the design guide - 

The original Equation 13 and Equation 14 for RisoN and RisoP are used now to calculate the parallel resistance of RisoP || RPE,P and RisoN || RPE,N. The values for RisoN and RisoP can be calculated by using Equation 21 and Equation 22.

just to re confirm, we would close SP and close the switch for Additional Resistor (From Earth to Negative) together. Then we would calculate RisoN || RPE, using equation  13.

Similarly  we would close SN and close the switch for Additional Resistor (From Earth to Positive) together. Then we would calculate RisoP || RPE, using equation  14.

Then we need to use

 Equation 21 and Equation 22.

RisoN and RisoP 

Now the input of AMC3330 is only 0 if PE is lost, otherwise we will measure the known resistance in parallel to RisoP/N, which will be always lower than the know resistance. .

Is our understanding correct ?

Hi Kanhaiya,

Yes your procedure is correct, but negative input voltages on the ADC are not expected. 
It should not be possible to get a negative input voltage at the ADC. It is possible however to have a negative voltage at the input of the isolated amplifier AMC3330, which is called VinAMC in the design guide.
I suggest to start testing with known values for RisoP and RisoN and checking if the system is performing as expected.


Best regards,

Andreas

 . Can you suggest any other ways we can verify our results, also you said we can get negative voltage at the amc3330 input ,(VinAMC ). but then we are just feeding the same voltage to 24 bit ADC which is communicating with MCU. would it impact the risop and rison value. We are still using your suggested modified equation - 

"Visolation =  VinADC* (RinAMC +Rst)/RinAMC *1/GainAMC

You don't need VRef in the calculation since the ADS131 has a differential input and you will get a negative reading via SPI if there is a negative voltage on the input."

Can you please provide us any method through which we can debug our issue and verify our test results ?

Hi Andreas ,

Yes i am sharing a rough diagram(Attach with this message) to get you an idea of our setup , there is one modification though instead of  6.81k res , we are using 11 (33.2k ) resistors from DC+ to S1  (of first switch ),and also from  DC - to S2 (of Second switch ). 

We will carry out the measurement , one more question ,in the first reply you said Quote "You don't need VRef in the calculation since the ADS131 has a differential input and you will get a negative reading via SPI if there is a negative voltage on the input." 

So we would get a negative voltage ?  this negative voltage will be used in derivation of VIsolation

becoz , (Visolation =  VinADC* (RinAMC +Rst)/RinAMC *1/GainAMC) ,

and then RisoP/N. which would give us both -/+ resistance....?

can you confirm  which values could be negative and which one should positive? 

Regards,

Kanhaiya 

IsolationMonitering.pdf

Hi Kanhaiya,

Thanks for sharing the diagram, this helps a lot.
Yes you will get negative voltage but that's okay, this will not lead to a negative resistance, this will cancel out in the formulas for RisoN/P.

Also for TIDA-010232 produces negative values for Visolation, since we subtract the reference voltage.

Best regards,

Andreas

Hi Andreas,

we have measured the voltage via probing and through ADC, There is no discrepancy however we noticed that when the Switches (TPSI2140Q) are turned on ,right after that ,the reading of Vin P/N (voltage across sense resistor) is more but after 3-4 reads it stabilizes.(Reduced and gived stable and has less voltage value)

i have prepared the excel sheet which contains manual calculator of RisoP & RisoN via the Formulas. (You can verify by providing the VINP/VInN values) and match with the Risop/n calculated via the ADC and compare with manual calculator.

And it also contains the reading of VInP ,VinN , we got from ADC VIA MCU, and calculation of VP,VN, RisoP/N value done via the firmware.

1. we are getting negative values as well as positive for VInP ,VinN. which is eventually giving us RIsoP & RisoN in negative sometimes.

2. There is some discripancy between Value of RisoN Calculated via firmware and via Excel Calculator .

why is that ? , our software flow is as following 

1. we take 10 readings of VInP closing P Side switch and calculate Vp

2. we take 10 reading of VInN closing N Side switch and calculate Vn

3. We ignore the first 4 reading (we noticed that after 3-4 reads it stabilizes)

4. then we take the Vp and Vn values from the above reading and calculate RisoP and RisoN 

for eg - RisoP & RisoN considered taking 5th reading Vp and Vn values will be one reading.

Can you please check the excel and our formula used in calculator , also please explain why we are getting negative resistance in calculator and also in ADC Calculation.Isolation Monitering Sheet.xlsx

Waiting for your valuable reply 

Thanks,

Kanhaiya  

Hi Andreas ,

We also tried one more exercise by connecting two100k one from DC- & one from DC+ to earth. Then we proceeded Measuring the RisoP & RisoN , but the values were no where near the 100K Values. (900k ) i have attached the sheet. Also when we removed earth still we were getting some resistance., but it was less then when the earth was present. (300k)

Earth Detect.xlsx

Hi Andreas ,

Any update on this above issue ? . we are still getting similar results after averaging the values  of Visolation and following the exact software flow with timing.

attached files shows the result , still getting some negative resistances and also the RisoP & RisoN Values are different, deviation is too much in case of RisoN. Can you suggest any changes or issue with our formula or setup ?

Isolation Monitering results (averaging).xlsx

Hi Kanhaiya,

To be honest I am not sure at this moment what the issue is in your setup. 
I think you need to debug this step by step. First lets do not use the Loss of PE circuit.

From the excel sheet I see that you are using RstN/P = 365 kOhm and RinAMc = 294 Ohm.

Please use two 100k resistors to simulate RisoP and RisoN.

Then please just close SP:
In this case the voltage at the input of AMC3330 should be 141 mV.
The voltage at the ADC input should be 282 mV.

Then open SP and close SN. In this case the input voltage at AMC3330 should be -141  mV
The voltage at the ADC input should be -282 mV.

Can you verify these voltages. 

If you put this in your excel sheet the calculation works as expected and you get 100k for RisoN and RisoP.




Best regards,

Andreas

Hi Andreas ,

We will try the above test you have recommended, externally using two 100k resistor connected from DC+ to Earth & DC- to earth. And then verify if we are getting the RisoP & RisoN value near to 100k

. One doubt is that you have used the calculator sheet we have sent , and i can see RisoP & RisoN Coming around 109k & -109K .

Is that correct value(not 100k)? also the resistance value is in negative is that ok ? . And do we expect same result via Firmware.

Hi Andreas ,

Thanks for the correction. we have revised the formula and yes now the resistance is in positive .We will retake the reading with External 100k Resistor to validate the Design. 

Meanwhile could you provide your simulation file. Tina TI /PSPICE/LTSPICE any format will work .We would modify as per our design and validate.

Regards

Kanhaiya 

Hi Andreas ,

Thanks for the simulation , we finally got our voltage same as the simulated circuit and we were able to get the 100k Value of RisoP & RisoN. Thanks for support .

We are testing for Earth loss now. In our circuit we have two additional switches which basically add 1.245 M Ohm resistor from Earth to DC + and Earth to DC- . We turned those two switches ON and then Measured the RisoP & RisoN Values.

Firmware Log are given Below When earth is present-  (using equation 13 and 14)

Vdc: 402.817230, Vp: 74.473371, Vn: -74.576750, RisoP: 1243689.968640, RisoN: 1245416.375310

As you can see we are getting values very close to the known resistor 1.245M Connected when earth is present .

Now when we removed the earth the Value are changed , as given below - (using equation 13 and 14.)

Vdc: 402.720520, Vp: 78.246364, Vn: -77.659671, RisoP: 1161596.654114, RisoN: 1152886.966650

How can we know for sure that the earth is absent ?

i would assume based on RisoP & RisoN Value?,

1. when value is not near the known resistance , the earth is absent ?

2. when value is near the known resistance , earth is present ?

then we tried the formula given in the TIDA-010232, that states some modification in the RisoP & RisoN Formula, we  implemented that.

 Equation 21 & Equation 22. 

But just to confirm our understanding .

The  RisoP || RPE, RisoN || RPE, are the value which will be obtained using equation 13 and 14. right ?

RPE,P & RNE,N will be 124500 Ohm(1.245Mohm) in our case ?

then we calculate the RisoP & RisoN Using Eq 21 &  22.

Please find the Firmware log for RisoP & RisoN values calculated via Eq 21 & 22 below ( when Earth is present)

1. Vdc: 402.909180, Vp: 74.563210, Vn: -74.538084,

RisoP: 1244535.065907, RisoN: 1244115.693987 (equation 13 and 14)

earthRisop: 3332614619.412250 earthRisoN: 1751570176.805691  (Eq 21 & 22)

2. Vdc: 402.854309, Vp: 74.474698, Vn: -74.635424,

RisoP: 1242599.989988, RisoN: 1245281.682253 (equation 13 and 14)

earthRisop: 644596055.826956 earthRisoN: -5503987846.279185  (Eq 21 & 22)

Please find the Firmware log for RisoP & RisoN values calculated via Eq 21 & 22 below (when Earth is absent)

1. Vdc: 402.939453, Vp: 77.862760, Vn: -77.973862,

RisoP: 1158267.654711, RisoN: 1159920.379793 (equation 13 and 14)

earthRisop: 16626360.388558 earthRisoN: 16973522.793565 (Eq 21 & 22)

2  Vdc: 402.849060, Vp: 78.513005, Vn: -78.400813,

RisoP: 1146516.876077, RisoN: 1144878.554049 (equation 13 and 14)

earthRisop: 14493990.988998 earthRisoN: 14236448.407788 (Eq 21 & 22)

In the above test also we are unable to get a conclusion on what basis should we consider that earth is absent or present?

Regards

Kanhaiya

Hi Andreas ,

Any update on the above issue ? 

hi Andreas ,

We have measured the  R_PE_N/P || RisoN/P using equation 13 and 14 , with known resistance 1.245 M ohm, when earth is connected we are getting values closer to  1.245 M ohm. But when earth is Disconnected 1.12 M ohm. Which as per your statement is not accurate. "Loss of earth can be detected if the measured value which is R_PE_N/P || RisoN/P is much bigger than the known resistor R_PE_N/P".

Can we connect on a call to have a short discussion ?

One more thing our earth and Digital GND is connected , will it impact the calculations ?

could you please provide your email address so we can connect ?

Hi Andreas ,

Waiting for your response .

Regards,

Kanhaiya 

Hi Kanhaiya,

What are the values for RisoN and RisoP in the test case when you have earth connected?

Connecting digital GND and earth should not have a negative impact on the measurement, but it makes the isolation provided by AMC3330 and TPSI2140 obsolete. In that case a non isolated solution would perform better.

Best regards,

Andreas

Hi Andreas ,

The values for RisoN and RisoP in our case is 1.245 Mohm, which we can enable via on Board additional switches.

Our setup looks like the simulation Attached.

Case 1.

SPST1 & SPST2 were enabled and Earth was present .

Then RisoP & RisoN was calculated via Eq 13 & 14 (On firmware)

Results.

 Vdc: 402.909180,

  Vp: 74.563210,

 Vn: -74.538084,

RisoP: 1244535.065907,

RisoN: 1244115.693987 

Case 2.

SPST1 & SPST2 were enabled and Earth was absent .

Then RisoP & RisoN was calculated via Eq 13 & 14 (On firmware)

Results.

Vdc: 402.939453

Vp: 77.862760,

Vn: -77.973862

RisoP: 1158267.654711

RisoN: 1159920.379793

Note - we are turning on both the SPST1 & SPST2 Simultaneously then measuring the RisoP and RisoN under Earth Present and Absent condition.

As you can see when earth is absent we are getting less resistance values of RisoP and RisoN (1.15Mohm) then the known Resistance 1.245 Mohm. 

This shouldn't be the case as per your suggestion, it should be much higher then known resistance ?

what do you recommend ?

Isolation Monitering Updated.TSC 

Regarding Isolation Monitoring.

Although we are getting Known Resistance when Connect known Resistance from Earth to DC+ & Earth to DC-. 

But when we remove these known value , and calculate the actual RisoN & RisoP

The values of RisoP & RisoN value seem to be increasing with time after turning on SP/SN.

Please find the Log for Measured RisoP & RisoN Values below. This samples are captured at every 5ms interval. Please validate logs.
Is there any timing limit that we need to consider samples till specific time after turn on SN/SP?

-----------VP-----------------------------
vdc, VinADC, VP


Isolation : 402.741821,0.577111,358.725567
Isolation : 402.712494,0.509821,316.898802
Isolation : 402.834595,0.445570,276.961416
Isolation : 402.784058,0.391628,243.431362
Isolation : 402.761169,0.339546,211.058106
Isolation : 402.818939,0.300888,187.028670
Isolation : 402.858002,0.263702,163.913877
Isolation : 402.848541,0.231420,143.847966
Isolation : 402.797485,0.200120,124.392372
Isolation : 402.791046,0.177902,110.581687
Isolation : 402.797882,0.156804,97.467495
Isolation : 402.806946,0.136903,85.097074
Isolation : 402.883392,0.117711,73.167871
Isolation : 402.813263,0.104934,65.225608
Isolation : 402.880127,0.093368,58.036206
Isolation : 402.800781,0.081272,50.517716
Isolation : 402.786163,0.069237,43.036651
Isolation : 402.831299,0.061932,38.495915
Isolation : 402.913269,0.056161,34.909043
Isolation : 402.904724,0.047613,29.595611
Isolation : 402.881561,0.040016,24.873554
Isolation : 402.807220,0.036261,22.539664
Isolation : 402.880127,0.034119,21.207952
Isolation : 402.835632,0.028544,17.742456
Isolation : 402.891022,0.023576,14.654659
Isolation : 402.868805,0.021728,13.505756
Isolation : 402.845520,0.020718,12.878146
Isolation : 402.828522,0.017174,10.675176
Isolation : 402.834320,0.013034,8.101813
Isolation : 402.844177,0.012853,7.989085
Isolation : 402.797607,0.013164,8.182334
Isolation : 402.862091,0.010558,6.562687
Isolation : 402.814972,0.007449,4.629906
Isolation : 402.847229,0.007448,4.629608
Isolation : 402.863403,0.008700,5.408118
Isolation : 402.858917,0.006492,4.035101
Isolation : 402.851562,0.003408,2.118424
Isolation : 402.912994,0.004349,2.703090
Isolation : 402.835785,0.005609,3.486520
Isolation : 402.803528,0.003786,2.353125
Isolation : 402.903412,0.000889,0.552606
Isolation : 402.871704,0.002419,1.503489
Isolation : 402.852875,0.004123,2.562925
Isolation : 402.872742,0.002599,1.615621
Isolation : 402.937469,0.000498,0.309257
Isolation : 402.876831,0.001278,0.794316
Isolation : 402.818787,0.002649,1.646487
Isolation : 402.788147,0.001640,1.019176
Isolation : 402.879333,-0.000092,-0.057259
Isolation : 402.914581,0.001318,0.819217
Isolation : 402.884583,0.002750,1.709114
Isolation : 402.819580,0.001407,0.874538
Isolation : 402.887207,-0.000946,-0.588244
Isolation : 402.948395,0.000233,0.145085
Isolation : 402.879333,0.002210,1.373912
Isolation : 402.823792,0.000954,0.593016
Isolation : 402.854462,-0.001113,-0.692026
Isolation : 402.911438,0.000142,0.088572
Isolation : 402.843811,0.001832,1.138614
Isolation : 402.823151,0.000736,0.457772
Isolation : 402.895111,-0.000789,-0.490427
Isolation : 402.859192,0.000337,0.209501
Isolation : 402.894989,0.002273,1.412979
Isolation : 402.897339,0.000237,0.147620
Isolation : 402.828125,-0.001303,-0.809674
Isolation : 402.801941,-0.000255,-0.158804
Isolation : 402.896545,0.001649,1.024693
Isolation : 402.918671,0.000346,0.215019
Isolation : 402.861694,-0.001340,-0.832638
Isolation : 402.821960,-0.000336,-0.208756
Isolation : 402.829834,0.002047,1.272665
Isolation : 402.886292,0.000611,0.379488
Isolation : 402.963257,-0.000724,-0.450018
Isolation : 402.895386,0.000022,0.013867
Isolation : 402.844727,0.001885,1.171866
Isolation : 402.768921,0.000723,0.449272
Isolation : 402.827759,-0.001850,-1.149797
Isolation : 402.929718,-0.000553,-0.343702
Isolation : 402.951172,0.001389,0.863354
Isolation : 402.841705,0.000332,0.206221
Isolation : 402.808533,-0.001366,-0.849189
Isolation : 402.871033,-0.000584,-0.363235
Isolation : 402.858124,0.000832,0.517416
Isolation : 402.819977,0.000549,0.341167
Isolation : 402.879181,-0.001024,-0.636258
Isolation : 402.838257,-0.000196,-0.121675
Isolation : 402.911285,0.001181,0.734075
Isolation : 402.797211,0.000141,0.087528
Isolation : 402.852356,-0.001452,-0.902272
Isolation : 402.839844,-0.000055,-0.034296
Isolation : 402.853943,0.001943,1.207652
Isolation : 402.832092,0.000441,0.274365
Isolation : 402.883392,-0.001036,-0.644161
Isolation : 402.858276,-0.000280,-0.174162
Isolation : 402.788544,0.001725,1.071961
Isolation : 402.830505,0.000562,0.349219
Isolation : 402.844849,-0.000796,-0.494602
Isolation : 402.819458,-0.000193,-0.119885
Isolation : 402.896820,0.001631,1.013509
Isolation : 402.860229,0.000611,0.380085
Isolation : 402.821686,-0.001116,-0.693666
Isolation : 402.861694,0.000250,0.155374
Isolation : 402.871033,0.001787,1.110730
Isolation : 402.943390,0.000615,0.382470
Isolation : 402.930756,-0.000484,-0.300907
Isolation : 402.904724,-0.000035,-0.021770
Isolation : 402.842346,0.001638,1.018430
Isolation : 402.765778,0.000787,0.489085
Isolation : 402.861816,-0.001439,-0.894519
Isolation : 402.947998,-0.000824,-0.512346
Isolation : 402.900360,0.001411,0.877073
Isolation : 402.840912,0.000500,0.310748
Isolation : 402.895782,-0.001052,-0.654151
Isolation : 402.860779,-0.000231,-0.143445
Isolation : 402.929993,0.001500,0.932244
Isolation : 402.864990,0.000671,0.417064
Isolation : 402.816162,-0.001233,-0.766283
Isolation : 402.954590,-0.000726,-0.451211
Isolation : 402.919312,0.000905,0.562597
Isolation : 402.866699,0.000401,0.249016
Isolation : 402.805237,-0.001548,-0.961917
Isolation : 402.909576,-0.000689,-0.428248
Isolation : 402.974335,0.001279,0.795061
Isolation : 402.902100,0.000458,0.284504
Isolation : 402.803009,-0.001293,-0.803412
Isolation : 402.881836,-0.000801,-0.497734
Isolation : 402.872223,0.001012,0.629101
Isolation : 402.868805,0.000821,0.510259
Isolation : 402.836304,-0.000634,-0.393952
Isolation : 402.825104,-0.000294,-0.182960
Isolation : 402.875366,0.001673,1.039902
Isolation : 402.894196,0.000154,0.095580
Isolation : 402.841827,-0.001368,-0.850382
Isolation : 402.842743,-0.000762,-0.473727
Isolation : 402.930389,0.001538,0.955803
Isolation : 402.859711,0.000516,0.320589
Isolation : 402.794983,-0.001248,-0.775677
Isolation : 402.826019,-0.000735,-0.456579
Isolation : 402.893524,0.001756,1.091495
Isolation : 402.928406,0.001074,0.667571
Isolation : 402.833405,-0.001375,-0.854408
Isolation : 402.805511,-0.000980,-0.609269
Isolation : 402.902618,0.002127,1.322319
Isolation : 402.899841,0.000993,0.617023
Isolation : 402.810364,-0.000634,-0.393803
Isolation : 402.788788,-0.000289,-0.179679
Isolation : 402.888672,0.001623,1.008887
Isolation : 402.782227,0.000658,0.409161
Isolation : 402.811951,-0.001170,-0.727514
Isolation : 402.884705,-0.000946,-0.588095
Isolation : 402.843262,0.001056,0.656388
Isolation : 402.789185,0.000516,0.320440
Isolation : 402.746033,-0.000872,-0.542020
Isolation : 402.841827,-0.000746,-0.463438
Isolation : 402.839447,0.001486,0.923744
Isolation : 402.808014,0.000918,0.570351
Isolation : 402.807739,-0.000786,-0.488787
Isolation : 402.873657,-0.000806,-0.500865
Isolation : 402.861694,0.001251,0.777914
Isolation : 402.817627,0.001036,0.643863
Isolation : 402.869995,-0.000708,-0.440326
Isolation : 402.834839,-0.000534,-0.331922
Isolation : 402.849976,0.001391,0.864696
Isolation : 402.846954,0.001021,0.634469
Isolation : 402.834991,-0.000932,-0.579447
Isolation : 402.820648,-0.000712,-0.442861
Isolation : 402.825775,0.001489,0.925832
Isolation : 402.862335,0.000783,0.486401
Isolation : 402.803284,-0.000525,-0.326256
Isolation : 402.812225,-0.000443,-0.275259
Isolation : 402.891693,0.001290,0.801771
Isolation : 402.854858,0.000465,0.288829
Isolation : 402.817230,-0.000791,-0.491620
Isolation : 402.795380,-0.000638,-0.396636
Isolation : 402.889465,0.001041,0.646994
Isolation : 402.845764,0.000548,0.340421
Isolation : 402.814178,-0.000893,-0.554843
Isolation : 402.932098,-0.000141,-0.087677
Isolation : 402.879852,0.001023,0.636109
Isolation : 402.818268,0.000724,0.449869
Isolation : 402.858398,-0.001062,-0.660116
Isolation : 402.810516,-0.000982,-0.610163
Isolation : 402.797882,0.000627,0.389926
Isolation : 402.806946,0.001061,0.659519
Isolation : 402.850372,-0.001137,-0.706788
Isolation : 402.788666,-0.001077,-0.669659
Isolation : 402.892609,0.001116,0.693666
Isolation : 402.837097,0.000931,0.578701
Isolation : 402.810913,-0.000551,-0.342360
Isolation : 402.872223,-0.001062,-0.659967
Isolation : 402.856018,0.000712,0.442264
Isolation : 402.751556,0.000542,0.336693
Isolation : 402.763153,-0.000458,-0.284803
Isolation : 402.878662,-0.000834,-0.518162
Isolation : 402.901703,0.001186,0.737355
Isolation : 402.837341,0.000907,0.563492
Isolation : 402.785767,-0.000535,-0.332816
Isolation : 402.735229,-0.000948,-0.589437
Isolation : 402.871307,0.001426,0.886168
Isolation : 402.837738,0.001362,0.846654

-----------VP-----------------------------
vdc, VinADC, VN

Isolation : 402.869049,-0.582783,-362.251129
Isolation : 402.903656,-0.505689,-314.330193
Isolation : 402.928131,-0.446595,-277.598427
Isolation : 403.011047,-0.390590,-242.786440
Isolation : 402.997467,-0.344344,-214.040466
Isolation : 402.912231,-0.298031,-185.252904
Isolation : 402.860229,-0.262949,-163.446108
Isolation : 402.816681,-0.230264,-143.129547
Isolation : 402.714203,-0.204016,-126.814237
Isolation : 402.837616,-0.176194,-109.520161
Isolation : 402.885895,-0.155262,-96.509310
Isolation : 402.950897,-0.136580,-84.896664
Isolation : 402.918671,-0.120750,-75.056514
Isolation : 402.868652,-0.103565,-64.374927
Isolation : 402.776154,-0.091231,-56.708369
Isolation : 402.784454,-0.081579,-50.708577
Isolation : 402.871948,-0.072465,-45.043394
Isolation : 402.885651,-0.061212,-38.048880
Isolation : 402.820770,-0.053919,-33.515299
Isolation : 402.780762,-0.048617,-30.219493
Isolation : 402.897614,-0.042682,-26.530480
Isolation : 402.875244,-0.036342,-22.589616
Isolation : 402.853668,-0.031861,-19.804218
Isolation : 402.834717,-0.029176,-18.135364
Isolation : 402.903137,-0.025649,-15.942981
Isolation : 402.851562,-0.021320,-13.252267
Isolation : 402.809845,-0.018797,-11.684063
Isolation : 402.812622,-0.017608,-10.944620
Isolation : 402.880890,-0.015532,-9.654509
Isolation : 402.958282,-0.012253,-7.616605
Isolation : 402.875244,-0.010452,-6.496928
Isolation : 402.794312,-0.010457,-6.500209
Isolation : 402.849579,-0.009996,-6.213319
Isolation : 402.974182,-0.007318,-4.548491
Isolation : 402.873016,-0.006108,-3.796374
Isolation : 402.813934,-0.006599,-4.101605
Isolation : 402.771423,-0.006400,-3.978439
Isolation : 402.900909,-0.004040,-2.511183
Isolation : 402.863281,-0.003383,-2.103066
Isolation : 402.799469,-0.004189,-2.604080
Isolation : 402.867096,-0.004372,-2.717404
Isolation : 402.863678,-0.002141,-1.330669
Isolation : 402.812225,-0.001332,-0.828164
Isolation : 402.905243,-0.002641,-1.641715
Isolation : 402.885101,-0.002619,-1.628146
Isolation : 402.848541,-0.000621,-0.386198
Isolation : 402.783539,-0.000197,-0.122271
Isolation : 402.886963,-0.001734,-1.077627
Isolation : 402.932220,-0.001989,-1.236580
Isolation : 402.884857,-0.000190,-0.118394
Isolation : 402.789581,0.000168,0.104378
Isolation : 402.832214,-0.001253,-0.778808
Isolation : 402.896942,-0.002081,-1.293540
Isolation : 402.919067,0.000048,0.029673
Isolation : 402.797211,0.000193,0.119736
Isolation : 402.748413,-0.000773,-0.480287
Isolation : 402.862213,-0.001809,-1.124747
Isolation : 402.960632,0.000027,0.016850
Isolation : 402.869598,0.000527,0.327747
Isolation : 402.804199,-0.000718,-0.445992
Isolation : 402.860229,-0.001019,-0.633127
Isolation : 402.864838,0.000352,0.218895
Isolation : 402.804047,0.000823,0.511452
Isolation : 402.850891,-0.001056,-0.656388
Isolation : 402.913147,-0.001552,-0.964601
Isolation : 402.851959,0.000432,0.268251
Isolation : 402.861298,0.000968,0.601962
Isolation : 402.799591,-0.000730,-0.453597
Isolation : 402.844452,-0.000807,-0.501909
Isolation : 402.935120,0.000251,0.155821
Isolation : 402.837219,0.000967,0.601217
Isolation : 402.900238,-0.000802,-0.498479
Isolation : 402.854187,-0.001048,-0.651169
Isolation : 402.921570,0.000428,0.266164
Isolation : 402.863281,0.001091,0.677860
Isolation : 402.841431,-0.000722,-0.448527
Isolation : 402.872223,-0.000633,-0.393206
Isolation : 402.816956,0.000335,0.208308
Isolation : 402.854309,0.000558,0.346833
Isolation : 402.867615,-0.000832,-0.517267
Isolation : 402.812622,-0.000976,-0.606585
Isolation : 402.865387,0.000644,0.400066
Isolation : 402.817230,0.000934,0.580490
Isolation : 402.834991,-0.000516,-0.320888
Isolation : 402.794464,-0.000688,-0.427800
Isolation : 402.861816,0.000105,0.065460
Isolation : 402.881042,0.000237,0.147620
Isolation : 402.797485,-0.000878,-0.545896
Isolation : 402.858276,-0.001143,-0.710366
Isolation : 402.900116,0.000609,0.378444
Isolation : 402.829987,0.001154,0.717225
Isolation : 402.827362,-0.000391,-0.242902
Isolation : 402.880768,-0.001185,-0.736759
Isolation : 402.817627,0.000854,0.530687
Isolation : 402.887482,0.001161,0.721400
Isolation : 402.798126,0.000082,0.050698
Isolation : 402.838806,-0.000839,-0.521591
Isolation : 402.821289,0.000708,0.440326
Isolation : 402.852478,0.001126,0.700078
Isolation : 402.887756,-0.000404,-0.251402
Isolation : 402.864990,-0.001283,-0.797447
Isolation : 402.858917,0.000116,0.072170
Isolation : 402.872101,0.001249,0.776124
Isolation : 402.816040,0.000105,0.065013
Isolation : 402.809845,-0.000879,-0.546195
Isolation : 402.797363,0.000123,0.076494
Isolation : 402.826294,0.001094,0.680246
Isolation : 402.854706,0.000100,0.061881
Isolation : 402.850647,-0.000830,-0.515925
Isolation : 402.797089,0.000294,0.182661
Isolation : 402.846161,0.001164,0.723786
Isolation : 402.813934,-0.000540,-0.335351
Isolation : 402.778137,-0.001393,-0.865740
Isolation : 402.878662,-0.000081,-0.050251
Isolation : 402.897339,0.000560,0.348175
Isolation : 402.801025,-0.000454,-0.282119
Isolation : 402.786285,-0.001356,-0.842926
Isolation : 402.801575,0.000439,0.273172
Isolation : 402.856812,0.001323,0.822647
Isolation : 402.880890,0.000281,0.174609
Isolation : 402.861694,-0.000755,-0.469253
Isolation : 402.836426,0.000298,0.185047
Isolation : 402.767212,0.001143,0.710217
Isolation : 402.874176,0.000036,0.022665
Isolation : 402.885101,-0.001468,-0.912412
Isolation : 402.865631,-0.000211,-0.131069
Isolation : 402.803528,0.000748,0.465227
Isolation : 402.748810,0.000063,0.039067
Isolation : 402.887482,-0.000417,-0.259454
Isolation : 402.944580,0.000127,0.078731
Isolation : 402.895508,0.000458,0.284803
Isolation : 402.831299,-0.000075,-0.046821
Isolation : 402.844330,-0.000766,-0.476112
Isolation : 402.928925,0.000071,0.044435
Isolation : 402.883392,0.000545,0.338632
Isolation : 402.810760,-0.000242,-0.150304
Isolation : 402.849579,-0.000788,-0.489682
Isolation : 402.853149,-0.000275,-0.171180
Isolation : 402.893005,0.001193,0.741381
Isolation : 402.856964,-0.000232,-0.144191
Isolation : 402.841553,-0.000564,-0.350561
Isolation : 402.778412,0.000067,0.041751
Isolation : 402.818146,0.001242,0.771800
Isolation : 402.894318,-0.000040,-0.024902
Isolation : 402.847076,-0.000884,-0.549326
Isolation : 402.793549,0.000350,0.217852
Isolation : 402.862213,0.001236,0.768072
Isolation : 402.835510,0.000407,0.252744
Isolation : 402.866699,-0.001337,-0.831295
Isolation : 402.861694,0.000029,0.017744
Isolation : 402.822205,0.001246,0.774633
Isolation : 402.837219,0.000218,0.135244
Isolation : 402.819458,-0.000924,-0.574377
Isolation : 402.901306,-0.000366,-0.227395
Isolation : 402.872467,0.000774,0.481331
Isolation : 402.781036,0.000258,0.160295
Isolation : 402.830780,-0.001408,-0.875432
Isolation : 402.928528,-0.000270,-0.167899
Isolation : 402.876831,0.001129,0.701718
Isolation : 402.852997,0.000701,0.435852
Isolation : 402.865631,-0.001126,-0.699630
Isolation : 402.865906,-0.000363,-0.225456
Isolation : 402.803284,0.001361,0.845908
Isolation : 402.828003,0.000422,0.262436
Isolation : 402.886566,-0.001280,-0.795509
Isolation : 402.850372,-0.000715,-0.444352
Isolation : 402.809967,0.000829,0.515180
Isolation : 402.773926,0.000793,0.493111
Isolation : 402.835632,-0.001139,-0.707831
Isolation : 402.898132,-0.000394,-0.244841
Isolation : 402.799316,0.001053,0.654449
Isolation : 402.789459,0.000588,0.365770
Isolation : 402.903015,-0.001312,-0.815341
Isolation : 402.935760,-0.000915,-0.568860
Isolation : 402.871033,0.000562,0.349368
Isolation : 402.782745,0.000390,0.242157
Isolation : 402.772736,-0.001013,-0.629548
Isolation : 402.936951,-0.000769,-0.477753
Isolation : 402.926422,0.001097,0.681886
Isolation : 402.816833,0.000657,0.408565
Isolation : 402.797485,-0.000729,-0.453298
Isolation : 402.889709,-0.000511,-0.317458
Isolation : 402.936432,0.000398,0.247674
Isolation : 402.889984,0.000507,0.315370
Isolation : 402.875366,-0.000293,-0.182214
Isolation : 402.803009,0.000179,0.111386
Isolation : 402.798126,0.000551,0.342658
Isolation : 402.799469,-0.000240,-0.149410
Isolation : 402.873657,-0.000335,-0.208159
Isolation : 402.934570,-0.000183,-0.113772
Isolation : 402.883545,0.000747,0.464333
Isolation : 402.804321,0.000164,0.101843
Isolation : 402.768280,-0.000212,-0.131516
Isolation : 402.825897,-0.000330,-0.204879
Isolation : 402.921417,0.000831,0.516671
Isolation : 402.888519,0.000230,0.142849
Isolation : 402.822357,-0.000763,-0.474174
Isolation : 402.831177,-0.000246,-0.152988
Isolation : 402.763397,0.000776,0.482077
Isolation : 402.753662,0.000923,0.573780


Vdc: 402.811035, Vp: 0.193206, Vn: -0.100364, RisoP: 1465843947.595337, RisoN: 761453281.076513 

Hi Andreas ,

Any update on the issue why the Vin ADC & VP values are decreasing over time after the switch is Turned ON ? I have also shared the log from our Firmware.

This would cause problem as we are having a wide range of data whose value is decreasing constantly with time, and we need to take average of 20 value from them to further calculate RisoP & RisoN .

Also request you to kindly share your email , so we can connect as this task of isolation monitoring is on priority.

Regards,

Kanhaiya

0638.Isolation Monitering Updated.TSC

Hi Kanhaiya,

Find the updated simulation below.
For  loss of PE detection you still need R_PE_N and R_PE_P but you also need some RisoP and RisoN in the simulation, otherwise there will be no closed loop.
The connection towards PE for R_PE_P and R_PE_N also needs to be a seperate connection to PE than the connection of RinAMC,
Also, you can never turn on SP and SN and at the same time, The results will not make sense.
The procedure is to turn on SP-> Measure VP -> turn off SP -> turn on SN -> Measure VN -> Turn of SN -> Calculate RisoP/N
The same is true if loss of PE detection is enabled. Just the calculation for RisoP and RisoN is different then.

Constantly decreasing voltages can appear if you keep measuring the voltage after the Switch is turned off, since the sampling capacitor of the ADC needs to be constantly recharged. Only do measurements while the switches are in the right configuration.


Best regards,
Andreas

Hi Andreas,

Thanks for the updated Simulation

The Constantly decreasing voltages appear even when the Switch is turned On. 

As you can see , even we have the kept the switch ON. The VinADC kept on decreasing with time.

What could be the reason for this effect , we are unsure about which of the 20 sample should be considered out of these decreasing values ?

Also should these value be stable or this effect will be seen?

We are following the procedure is to turn on SP-> Measure VP -> turn off SP -> turn on SN -> Measure VN -> Turn of SN -> Calculate Riso P/N.

but for Measurement of VP,VN we are taking 100 sample each, (The samples i had sent you earlier you can verify)

The behavior of VinADC kept on decreasing with time is observed when switch is Turned on and 200 samples(100 Sample VP & 100 Sample VN) are collected.

Regards,

Kanhaiya

Hi Andreas,

For isolation Monitoring , now we are applying 1.245 Mega ohm from Earth to DC- & Earth to DC+ using the addictional switches . Then we are calculating RisoP & RisoN which we are getting close to 1.245 Mega Ohm. which is nothing but (RisoN || RPE) &  (RisoP || RPE). 

Then we used it in the Eq 21 & 22 to obtain the Actual RisoP & RisoN values. 

then We keep a threshold at these Actual RisoP & RisoN value for warning and fault.

lets suppose that the actual RisoP & RisoN value drops to 500k , we would then get value (1.245Mohm || 500k)  then we can find out Actual RisoP & RisoN 

Using Equation 21 & 22 which would be 500k and then we could issue warning.

We are using this approach because by just using 2 switches , we were getting very high unstable Actual RisoP & RisoN Values.

Can we use this approach for isolation monitoring  ???

Hello Andreas 

Any update regarding the issue ? can we use this method ?

Regards 

Kanhaiya 

Hello Andreas,

Thanks for the confirmation on the procedure. 

In the design guide , i see there is a Test setup where in place of  RisoN & RisoP ,Resistor Bank are used .

And the set value of resistor bank will appear on Finding RisoP & RisoN.

Question is , have you guys removed those resistor bank and got a stable RisoP & RisoN Values ?

Like some stable value of RisoN & RisoP in Mohm ??

Regards,

Kanhaiya

Hi Andreas ,

Any update regarding the above case??

Regards

Kanhaiya