New owner of Tektronix THS710A, Questions & Discussions

[BravoV]

Jay_Diddy_B, yes, the P6117 insulation is excellent, as my close up shot shows the narrow & deep gap just for the ground cable clip. 

Mains voltage is 220V, any chance on helping me to answer my questions about the voltage ratings and using 1X probe above ?

[commongrounder]

I caught sight of this thread and though I would weigh in since I am an owner and regular user of a Fluke 199C scopemeter which is similar in function to your Tek THS unit.

On point #1:  It would be safe - on paper-  to use your scope to monitor a 220vac mains directly without 10x probe.  It is a bit nerve wracking though, because you do not have a very large amount of headroom for noise spikes.  There would only be 80vrms ac, and there could be peaks much larger than that coming down the line (think lightning strike or trees crossing lines).  The scope could handle some of this, but why risk it?  That is why I really like and use the 10x VPS2xx series probes that are used with the Fluke scopemeters.  They have accessory clips like alligator and spring grabbers that allow you to do what you are wanting with the multimeter leads and banana to BNC adaptor, but have the additional safety of a 10x probe, and the cat. rating that goes with.

Point #2:  The scope is isolated from ground, but there is a limit.  The internal breakover point between the isolated shell of the BNC and the scope system ground is up to 600 volts.  That is to protect you from floating the scope too high above ground and risking an arc-over that damages the scope - or worse yet -  you!

Point #3:  The 30 volt rms limit is what most safety agencies deem the maximum voltage exposure that a human can contact before electrocution becomes a possibility (I happen to think it is possible to get shock injured at much lower voltages under the right circumstances).  With uninsulated cabling or BNC connectors  they want you to limit the voltage that might be present at the two BNC shells to 30 volts to prevent accidental contact shock hazards (human safety).

The point of all of this is:  Use insulated accessories as much as possible.  Use Tek 10x probe as much as possible.   
If it were me, I would watch on e*ay for a Fluke VPS 2XX series scope probe with the accessory clips.  I have no qualms about connecting my Fluke directly to a power service entrance panel for 110v or 220v monitoring using these probes and the fat alligator probe tips.

Best of luck with your great find!

[alm]

The 'Fluke' isolated scope probes are made by Multi-Contact (the IsoProbe series). You might be able to find them cheaper without the Fluke brands. They may also have been sold by HP/Agilent at some point. The Tektronix P5102 offered a similar amount of protection, but is somewhat bulkier.

The P6117 (and later incarnations like the P2220) technically have insulated ground, but not enough to convince any safety certification lab (e.g. UL), so they're rated only for floating voltages that would be safe to touch. Connecting them to mains should be fine, but don't clip the ground clip to anything but ground (i.e. not mains or neutral), even though the manual may show examples of this and the scope would support it (with the correct probe).

[BravoV]

@commongrounder, thank you so much for the comprehensive explanations. 

About the VPS probe or IsoProbe branding as alm pointed out, thanks to both, I will start the stalking at ebay for cheap ones for sure. Just checked the price for new sets, its jaw breaking, way way too much compared to the price of my scope here. 

Ok, there will be no direct 1X probing for now and ever. 

Connecting them to mains should be fine, but don't clip the ground clip to anything but ground (i.e. not mains or neutral), even though the manual may show examples of this and the scope would support it (with the correct probe).

Wow .. please elaborate further why ? What is the worst case example ? You're starting to scare me now. 

If the ground clip can not be used, and only at ground, then how to observe/measure the signal properly between Live and Neutral ?   

So the scope's manual is kinda giving a misleading information ? Here quoting the example from the manual, its clearly shows we can use the ground clip at one of the mains plug, and NOT the ground.

[alm]

Connecting them to mains should be fine, but don't clip the ground clip to anything but ground (i.e. not mains or neutral), even though the manual may show examples of this and the scope would support it (with the correct probe).

Wow .. please elaborate further why ? What is the worst case example ? You're starting to scare me now. 

If the ground clip can not be used, and only at ground, then how to observe/measure the signal properly between Live and Neutral ?   

So the scope's manual is kinda giving a misleading information ? Here quoting the example from the manual, its clearly shows we can use the ground clip at one of the mains plug, and NOT the ground.

This picture is fine, as long as you use the P5102 probe. With the P6117 it's one of those things that will usually work fine, just like measuring means with those cheap DMMs, but this does not make it safe. It might be OK in hands-off measurements, but I would still be careful.

The P6117 is rated for 30 Vrms between the reference lead (ground lead is not really a good term for floating measurements) and earth ground. It assumes that anything connected to the reference lead would be safe to touch. This is not true for the neutral lead, which is why we don't make equipment with its chassis connected to neutral anymore. Electrical codes in general require the same amount of insulation for live and neutral conductors. If neutral conductor gets interrupted somewhere between the socket and the voltage on the neutral pin in the socket will rise to approximately mains voltage current limited to at least a few amps in most systems. Some supplier, the wiring systems (eg. ships) might have two live conductors and no neutral. And depending on the impedance of the neutral wire, a surge current may induce a voltage surge across this wire. Note that a CAT II 300 V input is designed for a 2500 V surge from a 12 ohm source. Do you expect the neutral to remain at earth potential under these conditions?

You can use the two channels in subtract mode (just like on a grounded scope) to measure across mains. I would use the P6117 probe only for floating measurements in CAT I systems, for example to measure relative to the positive power rail in a 12 V system. For power measurements I would get the Tek P5102 or the MC/Fluke isolated probes.

[BravoV]

So when it comes to probing common AC to low volt DC switchmode ps, the red zone (photo below) definitely out of my reach, right ?  Sorry, this sounds so noob, but when it comes to mains, just want to be really-really sure about this, and for sure I trust you.




Until I got P5102 or it's equivalent, no direct mains probing, period.

Alm, just realized that you've been helping and assisting me a lot on various T&M noob topics in this forum all this time, really appreciate that, thanks a lot. 

[PA0PBZ]

You probably want to stay away from the left side of that optocoupler also.

[qno]

measuring 240AC is not a problem. Its the probes. The 9 Meg resitor might lose some accuracy when using it over the rated voltage. The original high voltage probes are fully insulated. As long as you do not touch th metal BNC you are fine. You can even isulate them yourself by shrinking some shrinking tube over it. And if you do not trust yourself make it a double or triple layer. Only use the keyboard when measuring high voltage. Switch of the circuit when changing probe position.

[BravoV]

You probably want to stay away from the left side of that optocoupler also.

You're right, missed that part. Anything that is galvanically connected to mains is a no-no.

measuring 240AC is not a problem. Its the probes. The 9 Meg resitor might lose some accuracy when using it over the rated voltage. The original high voltage probes are fully insulated. As long as you do not touch th metal BNC you are fine. You can even isulate them yourself by shrinking some shrinking tube over it. And if you do not trust yourself make it a double or triple layer. Only use the keyboard when measuring high voltage. Switch of the circuit when changing probe position.

As alm said, I will do a total hands-off measurement if I desperately need to measure mains connected circuit. Thanks for the tips though.

[qno]

My software versions are 1.03 and 1.16.

Does someone know the difference between the 60, 100 and 200 MHz versions?

Is it software, Hardware or both?

[BravoV]

No idea, and I was googling for a while and still can't find anything about this THS700 series firmware. 

Even though there is a newer version, I don't see how we can upgrade it easily.

[SoundTech-LG]

Hi,

I agree with BravoV. I have been involved with the design of several Nimh chargers. The biggest challenge with Nimh is determining when the batteries are charged.

The biggest single problem is caused by not using enough charging current.

The Linear Technology LTC4010 datasheet gives some insight into charge termination methods.

Link to datasheet:http://www.linear.com/product/LTC4010

If you don't use enough charging current you do not see the negative dv/dt and you do not see the rapid change in cell temperature.

Jay_Diddy_B

The LTC4060 uses less external components.  http://cds.linear.com/docs/en/datasheet/4060f.pdf

The NiMh batteries work great. I just used the old battery as a donor for the contacts.

[Speleocaver]

I installed two 6 ah Li-ion batteries.  One battery plain, wired  in series with a li-ion protection circuit then attached to the second Li-ion battery.  Now the voltage is too high to power the scope, its 8.2 volts when fully charged and I dare not fry my Precious THS720.  I soldered 6 10A diodes in series. This would prevent THS720 charging the Li-ion's and keep them from EXPLODING! It also drops the voltage to 5.14 volts.  The replacement charging system is a small RC race car battery charger.  I use it for all my rechargeable projects like these... I have done this conversion DIY Li-ion mod  on a Irobot Roomba,  Underwater Dive light, 4 High power camera flashes, 2 portable radios, an Amp-meter,   All work GREAT!!
 .. it should have been perfect!  well apparently the THS720 has a very smart battery monitoring system.     As soon as I hit the power button It checks out the source and rejects it, Lights up shuts down,  tried more voltage...5.5v less 4.8v no go.  Or it could be the Li-ion battery protection circuit,  it cuts power around 2 amps, the scope draws 1.89A calculated.  Either that or the scope senses that it cannot charge the battery because it has no reverse resistance... because of the diodes... What a bummer...  If it does not act like a ni-cad or ni-mh maybe it won't work... Perhaps?

SO, I put in 4 loose nimh 4ah and soldered the red lead to the top + ( I had to open the case to get the red out) closed it up then stuffed some neoprene rubber to push the battery down into the - spring.  Worked great! New batteries for $15 or Factory Rippoff $200.

In the meantime I will try to run the scope again this time without the protection battery protection circuit and the meter will be given full current but still through the voltage drop diodes. If it happens to work this time then I will need to see If I can parallel the protection circuits to get 4 amps.  The Li-ion's would double run time if I can get them to work...
   
Rich

 Voltage: 3.7v
    Capacity: 5800mAh
6.8cm x 2.5cm - 2.67inch x 0.98inch
26650 battery

[BravoV]

Rich, thanks for sharing this, I was curious too on how it performs using Li-Ion, keep us updated if you still pursuing for alternative battery for this scope. 

[Zucca]

Looks like now we have the schematics... 

https://www.eevblog.com/forum/testgear/tektronix-ths700-tekscope-component-level-information-package-and-schematic/

[hibone]

The keysight U1561A Passive Probe are 10x with 250 MHz BW and cost about 150 €
They are rated Cat II 1000V and Cat III 600V thus they may be a valid replacement.

The only issue may be the compensation range.

Suggesting other models may be useful since P5102s are discontinued and cost about 250 €