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| Help needed - Siglent TPA10 / Tektronix TekProbe offset not working |
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| FlexibleMammoth:
Hi all, I own some Tektronix active probes (ADA400A and P6247) that still use the TekProbe interface [1]. I have quite a hard time to get them running with my Siglent SDS5000X via the official Siglent TPA10 TekProbe adapter [3]. In particular, I am unable to do any offset adjustment, and I have a suspicion that my adapter is defective. I realized I went into way too much detail, so here is the short version: Could someone who owns EITHER a Tektronix Oscilloscope with a TekProbe interface OR a Siglent Oscilloscope with a TPA10 adapter please measure the voltage present at the offset pad of the TekProbe interface? - Does the voltage change at all when you rotate the offset button? - What is the voltage range when adjusting the channel position to min/null/max? -------------Rambling and lengthy debugging below---------------- Info: Both probes support manipulating the DC offset. The ADA400A supports manual offset adjustment, while the P6247 offers DC Reject. Info2: The mechanism by which the TPA 10 generates its offset is the following (provided by Siglent): --- Quote ---The mechanism of the scope controlling the offset over TPA10 is that the scope programs an offset DAC in the TPA10, and the TPA10 outputs the offset to the Tek's probe thru the TekProbe interface level II. If the offset is correctly added to the front end of the probe, then it can be captured and displayed on the scope. --- End quote --- What I tried: ADA400A: 1) When DC offset is enabled on the probe: - The ADA400A allows manual adjustment on the probe itself. - The offset control of the scope does not work. 2) When DC offset is disabled on the probe: - The ADA400A no longer controls the offset, but neither does the scope. - The offset control of the scope does not work. I think this expected due to the limited interface on this probe; there are only 4 wires going from the probe to the TekProbe connector (+/-15V, +5V, attenuation ID), so the offset voltage is ignored. P6247: 1) When DC reject is enabled on the probe: - The P6247 rejects DC and shows correct signals. - The offset control of the scope does not work. 2) When DC reject is disabled on the probe: - The P6247 shows a constant DC offset of about 1.2V, which I assume means it is crashing into the V+ rail of the input transistor. - When applying the input calibrator of my scope to the probe input, i can see a faint square wave riding on top of the 1,2V DC offset. - The offset control of the scope does not work. To find out what is going wrong, I measured the offset pad in the tekprobe adapter. It is always sitting at 2.5V, no matter how I adjust the offset. That seems strange to me, since for the 1103 Tekprobe power supply, Tek adjvertises a +-1V offset range [2]: --- Quote ---Outputs Pin 1: n.c. Pin 2: n.c. Pin 3: +5 V. Pin 4: +15 V. Pin 5: Offset ±1 V. Pin 6: –5 V. Pin 7: –15 V. --- End quote --- The adapter works the same way (taken from [3]): --- Quote ---Specifications Bandwidth 4 GHz Power Supplies +15 V (±2%, 100 mA), -15 V (±2%, 100 mA), +5 V (±2%, 200 mA), -5 V (±2%, 200 mA) Offset Voltage -1.2 V ~ +1.2 V to the probe. Multiply it by the attenuation factor of the probe to calculate the system offset range. --- End quote --- Now if the offset works the way I think it works, a fault where it is 2.5V all the time would surely cause the probe to crash into Vmax. Could someone who owns a Tek Scope with a TekProbe interface please measure the offset pin? What is the voltage range? Does it change when you rotate the offset button? If someone has a Siglent TPA10: Could you verify if your adapter behaves the same way? What is the voltage range? Does it change when you rotate the offset button? Thanks a lot, BR Andreas [1] https://www.tek.com/en/support/faqs/what-tekprobe-interface [2] https://www.tek.com/en/datasheet/probe-power-supply-1103 [3] https://siglentna.com/wp-content/uploads/2021/10/LPA10_TPA10_Datasheet_DS060APA_E01A.pdf |
| FlexibleMammoth:
I edited the original post to get straight to the point - the lengthy introduction was obfuscating the problem. :blah: If someone has a Tek scope with TekProbe interfaces or a Siglent TPA10, a simple voltmeter measurement would help a lot :) |
| tautech:
From an email last year to Siglent EU from Siglent DSO product manager.....I think about this issue for you: The mechanism of the scope controlling the offset over TPA10 is that the scope programs an offset DAC in the TPA10, and the TPA10 outputs the offset to the Tek's probe thru the TekProbe interface level II. If the offset is correctly added to the front end of the probe, then it can be captured and displayed on the scope. • If the TPA10 is connected to the scope without any probe, then the offset feedback loop is not created, so what the tester saw is on purpose. • As for the case that with the ADA400A probe, we guess its offset is not provided from the TekProbe interface level II , but controlled by manual (we checked the probe user manual and found it has offset control button on probe, see figure below). If our guess is correct, then what the tester saw is on purpose. However I have raised this again with some contacts and it may be a day or 2 before we get replies. |
| TimFox:
I have a Tektronix power supply/adapter for TekProbe. The "offset" pot does not function with some of the Tektronix TekProbe probes. |
| alm:
--- Quote from: FlexibleMammoth on February 09, 2022, 01:20:45 pm ---Could someone who owns EITHER a Tektronix Oscilloscope with a TekProbe interface OR a Siglent Oscilloscope with a TPA10 adapter please measure the voltage present at the offset pad of the TekProbe interface? - Does the voltage change at all when you rotate the offset button? - What is the voltage range when adjusting the channel position to min/null/max? --- End quote --- I have a Tek TDS3052, which may not support the TekProbe offset feature. From what I remember reading in catalogues, the P6243 single-ended FET probe, which does not have the offset feature, is recommended for the TDS3000 series, while the P6245 probe, which does support offset feature, is recommended for the TDS600/700 etc. I measured pin 5 as indicated by the attached diagram without a probe connected, and it stayed at 0V regardless of the setting of the offset control. The offset control also works with simple passive probes. Note that this offset feature is separate from the vertical position control. The way the manual describes it, it can prevent the scope from clipping a signal that's out of range, so clearly the offset is applied in the analog input circuit. As far as I know, it controls the offset voltage fed into the vertical amplifier. It might be that when it detects an active probe with offset feature, it supplies a voltage on pin 5 instead, but it's quite hard to measure while a probe is attached, since the case covers the area around the connector. I'm guessing this is different in the scopes that do support supplying an offset via the TekProbe2 interface, but I don't have access to such a scope. I do have an ADA400A, and when the offset switch on the ADA400A is on, both the offset pots on the ADA400A and the offset control on the scope affect the vertical position of the signal. With the offset off on the ADA400A, only the offset control on the scope affects the vertical position. |
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