Fil, Georgia
Luis sent us some D25 M-F boxes, which go between the PZT driver chassis and the cable to the feedthrough, with modifications to balance the strain gauge readouts for the P-SAMS (ZM2, ZM4, ZM5). In the current configuration the strain gauge voltage is most often >10V, see for example Lee's table here. This change only affects the strain gauge readout, nothing else.
We approximately followed the test procedure (E1200534). We took measurements of resistance and voltage across the SG and bridge excitation, SG to ground and bridge excitation to ground before and after adding the modified breakout board Luis sent, with a trimpot between pins 11 (SG) and 12 (bridge excitation) of the D25 piezo driver chassis. We tuned the trimpot to get the SG voltage at the nominal drive (100V to the PZT) as close to zero as possible. Then Fil took the modification board and soldered in the closest resistor to our ideal trimpot value. We then took measurements of the SG voltage as a function of PZT voltage, driving the PZT using a voltage calibrator at the two drive inputs to the D15 on the chassis.
I scanned in the filled-out test sheets we used at the racks, and put them on the DCC here.
We were successful with ZM2 and ZM5, ZM4 is a bit strange.
ZM2
Without the modification box the resistance between pin 11 and 12 on the D25 was 357.5 Ohms, after tuning the modification board voltage was minimized at 100V of drive to the P-SAMS the resistance was 95.3 Ohms. I've plotted the strain gauge voltage vs PZT drive voltage in the first attachment, and also attached the code with the numbers. Sweeping the PZT from 0V to 118V, the strain gauge voltage goes between 0.412V and 2.057V.
ZM5
I forgot to measure the "before" resistance for ZM5, after Fil's adjustment we measured 82.5 kOhms across the SG to bridge excitation. Sweeping the PZT from 0 to 118 V the strain gauge voltage goes between -2.234V and 0.265V (see second attached plot).
ZM4
We've noticed in the past that the ZM4 strain gauge has a sign flip compared to ZM5 (see the table in Lee's earlier alog). Without the modification box the SG voltage was -8.7V, adding the breakout board with the trimpots the SG voltage became large and negative! With the trimpot at 82kOhms the ZM4 SG voltage read -22V for 0V PZT drive, with 181kOhms on the trimp pot it measured -16.8V for 0V PZT drive. I'm not sure I understand what's going on here.
The breakout board with the pots are connected to pins 11 and 12(Axial Strain), this is good when the higher resistor value is between pins 11 and 12 as in ZM2 and ZM5, but in ZM4 the higher resistance is in pins 11 and 24, having the pots in the original connections will affect the output voltage since we will reducing even more the axial resistance which at the end I believe will increase the negative voltage see at the output. Please modify the pot connections in the board by disconnecting pin 12 and adding this one to pin 24, then you can try to balance the strain gauge. The new resistor will need to be place it between pins 11 and 24 in the box.
Thanks Luis! Fil modified the pot connections so we re-balance rather than unbalance the strain gauge. I tuned the breakout-board-pot to make the strain gauge voltage close to 0V when there is 100V to the piezo, the resistance between pins 11 and 24 was 89.4 kOhms. Fil then soldered the resisters into the modification box and this is now installed on the chassis. The strain gauge voltage vs Piezo voltage plot is attached, and I modifed the DCC test results entry (E2100536) to include the new ZM4 box.
This afternoon Vicky and Sheila are in HAM7 taking more beam profile measurements and will get some data so we can calibrate the new strain gauge readouts to mD.