| Electronics > Projects, Designs, and Technical Stuff |
| DIY DC Current Probe? |
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| Brutte:
--- Quote from: Jeroen3 on September 23, 2017, 04:02:43 pm ---Now, the immediate problem that arises when you're using a shunt is that the scope ground lead will be mains earth referenced. --- End quote --- You did not mention the bandwidth and the voltage bareer needed I think. If that is for in-circuit measurement of something that is mains powered then I would rely on some isolation. OTOH if that shunt is just floating around common mode +-1V (earth lead voltage drop) then I think you could use a raw op-amp with 5-resistor arrangement. In this post I mention one with +-300V common voltage /100 and 1V diff voltage so a bit of overkill in your case. I suggest you could start from +-10V common voltage /5 and 10mV diff shunt voltage amplified to 100mV for scope. For 1MHz bandwidth you need a 50MHz GBW opamp then. And some decent resistors. |
| ajb:
Interesting! Looks like some of those resistors were laser trimmed? What's the back of the sensor look like? They actually sell an SOIC version of their sensor that is intended to sit over a PCB track that carries the sensed current, but it's only spec'ed for DC to 500kHz. I'm not sure if the lack of a well-controlled substrate is part of that limitation, maybe they're just unable to package sufficient analog circuitry. https://www.sensitec.com/products-solutions/current-measurement/cfs1000 |
| Jeroen3:
I think you really need die better parameters of the ceramic for this to work. The laser trimmed resistors are probably the only way to get the precision they advertise. Because I see no programmable parts. Now, does anyone know of a -12V and +12V SMD LDO pair? |
| Assafl:
Perhaps a belated reply but I needed a similar sort of setup for detecting motor current. Ended up using an Allegro ACS712 (which have been discontinued and now are called ACS723). Similar thing albeit cheaper. Also seems to be more finicky (but doesn't need the dual polarity power supply). Why not use a 12V LDO and a voltage inverter like http://www.ti.com/product/lt1054/datasheet ? I like the TPS60400DBVR voltage inverter which is in an SOT23 package but it is only up to 5V... |
| capt bullshot:
--- Quote from: Jeroen3 on September 26, 2017, 01:09:29 pm ---The CMS3005 is here. So, whats on it? --- End quote --- Looks quite the same as their predecessors (CMS20xx), except for the faster OP-Amp. I should ask them if they use a different sensor chip (that's where their knowledge is). The CMS2000 series is somewhat comparable to the LEM closed loop sensors, some aspects were better with the CMS, others with the LEM LA-100 (e.g.) In the early days of the CMS2000, they were quite useful as thermometers :-) |
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