This morning, I decided to adjust RCAV's temperature setpoint (C3:PSL-RCAV_RCPID_SETPOINT) up by 1 Kelvin. As I saw not much change in the readout of the PT1000 sensor overnight, I'm afraid that the signal might be too small for a 0.1 k change.
We might be able compare the readout from C3:PSL-GEN_DAQ16 to C3:PSL-FSS_SLOWDC level. SLOWDC controls the temperature of the NPRO crystal for adjusting laser frequency.
The calibration for SLOWDC is 4700 MHz/V*. The resolution of SLOWDC is 0.0001 V => 0.47 MHz.
Use df/f = dL/L to compute the equivalent cavity's length change, dL ~ 3 e-10 m.
Compare this dL to the effect of thermal expansion of the cavity.
dL = alpha x L x dT =>
3 e-10 [m]= 0.51 e-6 [1/K/m] x 0.203 [M] * dT [ K]
dT [K] = 3 milliKelvin is the resolution of the temperature we can measure, so we should be able to measure 1 K change on the cavity easily, and we can compare with what we see on the sensor.
From above equations, the cavity's temperature is related to SLOWDC by
dT = dV_slowdc x 32.91 [K/V].
For 1 kelvin change on the cavity, SLOWDC should change by 0.0304 [V]
Cavity's parameters
cavity's length, L = 0.2032 [m]
SiO2 expansion coeff, alpha = 0.51 e-6 [1/K/T]
channel list:
C3:PSL-RCAV_RCPID_SETPOINT set temperature for PID cavity's thermal control
C3:PSL-RCAV_TEMAVG average temperature on the outside surface of the can
C3:PSL-FSS_SLOWDC thermal control on laser's PZT for adjusting frequency
C3:PSL-GEN_DAQ16 readout from the temperature sensor on the top seismic stack
* About the calibration, I used sidebands (35.5MHz x2 =71 MHz) to calibrate SLOWDC to frequency. I also used the cavity's free spectral range (737 MHz) for comparison as well. The results agree well. |