1
\$\begingroup\$

I am trying to convert the output of a photomultiplier tube module (Hamamatsu HC120) which ranges from 0 to 10V to +-10V in order to fit the full dynamic range of a ADC (MCC USB-205). To do so, I've implemented the circuit below using a TI TL074CN op-amp in order to substrat 5V with a gain of 2. The following values are used:

V1: signal 0-10V

V2: 5V

R1: 1.5 kOhm

R2: 0.75 kOhm

R3: 1.5 kOhm

R4: 3 kOhm

U1 : 12V

U2 : -12V

enter image description here

Initially, the signal voltage was set from 0 to 10V using an ajustable DC power supply, the output gave the correct +-10V range. However, when connecting the PMT module, the output of the circuit will only range from -10V to 5.5V.

At this point I've kind of run out of ideas to what could cause this. Some hypothesis I have included grounding problem or some current limitation from the sensor that saturates the output. I however lack the theoretical electrical engineering background to properly assess the problem.

How can this problem be solved?

Edit:

Here are the full connections schematics. As shown, I've grounded everything together. Could this be a source of the problem?

enter image description here

Datasheets:

USB-205 ADC https://www.microdaq.com/downloads/dl/file/id/79/product/900/measurement_computing_usb_200_series_data_sheet.pdf

Hamamatsu HC120 https://mi-lasers.com/wp-content/uploads/HAMAMATSU-HC120_series.pdf

TL074CN http://www.ti.com/general/docs/suppproductinfo.tsp?distId=26&gotoUrl=http%3A%2F%2Fwww.ti.com%2Flit%2Fgpn%2Ftl074

\$\endgroup\$
  • \$\begingroup\$ A good starting point would be providing a link to the datasheet and describing in detail the connections. Your problem might be the output resistance of the sensor you're trying to use, in this case an INA amplifier would be better than an opamp \$\endgroup\$ – valerio_new Jun 30 at 20:13
  • \$\begingroup\$ BEFORE you send signal into op amp, you should buffer sensor line to make sure there is (almost) no current draw from the sensor line. You may very well be pulling current from sensor, dropping its output voltage \$\endgroup\$ – Ilya Jun 30 at 20:15
  • \$\begingroup\$ just glanced at the datasheet: your amp is also NOT rail-to-rail, it doesn't go all the way to positive supply rail (12-13.5V with V+ = 15V). You're losing a little to that too. Find a rail-to-rail op amp as well! \$\endgroup\$ – Ilya Jun 30 at 20:19
  • \$\begingroup\$ I will give more detailled information on the connection, I'm working on the schematic. @Ilya, when you talk about buffering the sensor line. Does this simply mean adding a unity gain amplifier before my level shift amplification? \$\endgroup\$ – Marc-Antoine Jun 30 at 20:33
  • \$\begingroup\$ @Marc-Antoine exactly that \$\endgroup\$ – Ilya Jun 30 at 20:42

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Browse other questions tagged or ask your own question.