OWON SDS7102 calibration - Page 1
Forum section: electronics / testgear

author: akis
author_rank: Frequent Contributor
timestamp: August 12, 2014, 07:06:26 pm
content: The scope shows 9.850V, the PSU shows 10.0V and the mains powered digital multimeter shows 10.021V.Therefore I calibrated the scope 10 times, to no avail. Unplugged mains, recalibrated, connected 50Ohm terminators, nothing seems to do it. It is off.Does anyone know how to go about this?

author: jpb
author_rank: Super Contributor
timestamp: August 12, 2014, 08:37:32 pm
content: The dc gain accuracy from the spec sheet is +-3% so for 10V any value between 9.7V and 10.3V is in spec.Recalibrating may not make much difference if the internal voltage reference (which is used for the calibration) is itself out.Oscilloscopes are notoriously inaccurate, there are lots of posts on here from people who have just discovered that their (sometimes quite expensive) scope is out. My WaveJet is surprisingly accurate (the Japanese tend to be very accurate when they build things) but the spec is still quite loose.

author: onlooker
author_rank: Frequent Contributor
timestamp: August 13, 2014, 03:46:17 am
content: I agree, for the numbers you showed, you should not need or want to do a manual calibration.On the other hand, from what I have tried, the auto calibration affected mostly the zero-offset calibration and had not-so-clear effects on the gain (v scale) calibration. If your gain or trigger level calibration is really off, you can do a manual calibration.I recently had to go through the tedious manual calibration process for my SDS7102V the hard way and the process I am about to describe is unofficial and likely incomplete or less than optimum. There is no guarantee it will work on your scope properly.For simplicity, I will list the steps for the fine level gain calibration, which can be done somewhat from the scope's front panel. The coarse level calibration is much more tedious and is likely not needed. It is also assumed that the offset calibration (before doing auto calibration) is in a good standing.---Prepare for the fine level gain calibration:1). Backup your tx.txt file from the scope to a PC:The calibration data is stored in a file named tx.txt on the scope. As others have discovered, Owon's firmware updating software provided undocumented options to encrypt and download tx.txt files from a PC to the scope, but there is no easy way to do the backup to PC (for what I know). I myself have no such need since my starting point is that the tx.txt file (and the firmware) on the scope had already been corrupted.2). Activate the scope front panel calibration options:Edit the PC version of the tx.txt file to have$trigmode control_send=1; //from 0;Then, download the tx.txt to the scope and restart the scope.3). Something to know before doing front panel calibration:3.a). The buttons "50%" "force" "ch1_V" "ch2_V" "math" "save" "Vpos1" and "Vpos2" are ready to be used to adjust, quit and temp save some of the screen adjustable calibration.3.b). The gain calibration is per channel and per channel mode(dual or single)3.c). Notations used,<C> -- channel id, can be 1 or 2<!C> -- id of the channel other than <C>, can be 1 or 2<S> -- vertical scale (Volt/Div) setting, can be one of 0(2mV),...,11(10V)Vscl<C> - volt/div (v scale) dial for ch <C>.Vpos<C> - 0 voltage position dial for ch <C>.----Perform front panel gain calibration: (aka Full Scale Voltage Value)This is to have the V scale of the displayed waveform match the actual V scale of the waveform presented on the BNC input.Parameters: (total=72)$adc_conf_FullScall_ch<C>_<S>=<val>; //dual ch mode, ch1(2)$adc_conf_FullScall_merge_Ch<C>_<S>=<val>; //single ch1(2) mode, the ch1(2) ADC$adc_conf_FullScall_ch<!C>toCh<C>_<S>=<val>;//single ch1(2) mode, the ch2(1) ADCProcedures: All operations are on the scope unless stated otherwise.Let's use ch1 V scale8(1V/div), as an example1). Preparations:set Vscl1 to 1V/div scale, AC all.Have the Vk(rms) measure shown.Connect the scope to a FG capable of ,say, 1kHz symmetrical square wave.(A VDC can be also used too and with DC coupling and measurement)Parallel a DMM at the channel 1 input BNC, and set it to measure ACV.Adjust the FG's output to show about (+-)4V on the DMM.2). Calibration of ch1 in the dual channel mode:Turn on both channels.Multi-press "50%"/"force" until "Adjust ADC_conf_FullScale" is shown.Adjust Vpos1 until Vk(RMS) showing the same value as shown on the DMM.Copy the FullScall_ch1= value shown (say,301) on the scope to the tx file on PC as$adc_conf_FullScall_ch1_8=301;3). Calibration of ch1 in the single ch mode:Turn on ch1 and turn off ch2.Multi-press "50%"/"force" until "Adjust ADC_conf_FullScale_merge" is shown.Adjust Vpos1 and Vpos2 until the Vk(RMS) showing the same value as on the DMM and the trace is the thinnest possibleCopy the last value shown when turning Vpos1 (say, 296) to the tx file on PC as$adc_conf_FullScall_merge_Ch1_8=296;Copy the last value shown when turning Vpos2 (say, 297) to the tx file on PC$adc_conf_FullScall_ch2toCh1_8=297;4). Repeat the steps above for all channels and all V scales with FG outputting a near full scale signal for any given scale.5). Download the resulting tx file from PC to the scope.----Finalize:After the calibration, a finalized tx file sending to the scope needs to have$trigmode control_send=0;