Oscilloscope needs some calibration - Page 1
Forum section: electronics / beginners

author: huggy
author_rank: Newbie
timestamp: August 01, 2014, 11:54:27 am
content: Hi, i'm new here on the forum but not from the youtube channel. Just got my first oscilloscope, it's an Hitachi V-212. I got it cheap for £20 from a university. I've got the service and operator manuals in pdf format.As you can expect, it's a learning curve and i've got the basics covered. Problem is the scope needs some tweaking for calibration i think. I measured a 5 volt supply coming off a regulator and on my multimeter that gave me a reading of 5.04v. On the scope i set the division to 1v and check it but i'm getting a reading of about 6 volts or thereabouts and it's consistently wrong with other voltages too. Now am i right in saying that it's the vertical amplitube gain that or dc offset that needs calibrating?Also the dc balance is off as well but i'm getting confused with adjusting this as everytime i set the dc bal pot and obviously go back to the cal div of 5mv, the trace needs repositioning and i'm sort of back to square one. The manual says to initially set the cal div to 5mv then position the trace to centre graticule, then switch up to 10mv. It's at that point where the trace goes up a slight bit and i then adjust the dc bal.

author: w2aew
author_rank: Super Contributor
timestamp: August 01, 2014, 12:06:42 pm
content: Quote from: huggy on August 01, 2014, 11:54:27 amThe vertical gain and DC offset (balance) are two different things. The DC balance control is used to adjust the baseline so that it doesn't change with the volts/div setting. As the manual says, set it to 5mV/div, use the vertical POSITION control to move the trace to the center graticule, then switch it to 10mV/div and adjust the DC balance trimmer to put the trace back on the center graticule. Often times you have to iterate on this process a few times. Once that is set, then you can look at the vertical gain adjustment...

author: huggy
author_rank: Newbie
timestamp: August 01, 2014, 01:25:55 pm
content: I must be doing something fundamentally wrong because after about 4 iterations of the process i end up with the Y position knob at its right most position on centre graticule.This is what i'm doing step by step.Machine turned off.Set all dials, knob ands switches to their default state as in the service manual and also the cal pots including the 5mv/div (cal) on ch1 and ch2 in their cal positions.Turn on machine and wait for warm up.1. centre the trace using the y position knob.2. switch volt/div to 10mv.3. trace goes up a little so i turn the dc bal to make the trace centred.4. now i switch the volt/div back to 5mv and the trace goes slighly below the centre so i adjust the y posistion knob for centre trace.5. now the y position knob is off centre to the right.6. I go through the 1 - 5 process a few times and end up with the y position knob too far off centre to the right after centering the trace on 5mv volt/div.I must be doing something wrong in the process surely.

author: Andy Watson
author_rank: Super Contributor
timestamp: August 01, 2014, 01:44:31 pm
content: You should be adjusting the DC bal tominimisethe change when you switch ranges on the amplitude. The change will be most sensitive on the switch between 5mV and 10mV. Note - that's minimising thechange- this is not the same as chasing the trace back to the centre line. As mentioned above, you may have to make several iterations - if only to determine the orientation of the DC bal with respect to the direction of change - note the direction will change as you go through the minimum.

author: w2aew
author_rank: Super Contributor
timestamp: August 01, 2014, 02:27:56 pm
content: Quote from: Andy Watson on August 01, 2014, 01:44:31 pmYes - what Andy said! Don't touch the vertical position control after the first time. Just switch back and forth between 5 and 10mV/div, adjusting the DC balance to minimize the change in the trace position. You may not be able to get it perfect...

author: Kennynva
author_rank: Newbie
timestamp: November 28, 2016, 06:18:16 pm
content: Quote from: huggy on August 01, 2014, 01:25:55 pmYou have to switch the time/div knob all the way to the right to X-Y setting...and it should be a small dot in the center of the screen..and then you set each channel volts to 5mv then switch it to 10mv..and if it moves then the adjustment can be made..