we started with an analysis of the behavior that occurred during the shift on Sunday 15th. All the relevant signals (described in https://logbook.virgo-gw.eu/virgo/?r=56251) are shown on the attached plot.
In the plot it can be seen that the voltages (V_IN, V_OUT) and current (I_OUT) are consistent with the command voltage (CHROCC_V_DAC channel). Instead the trend of the heater temperature (TE_IntHeater channel) is strange: when at a certain point the DAC control voltage is manually increased (from 0.38V to 0.42V), it happens that for the first few minutes the heater temperature decreases by about 7C instead of increasing immediately. Furthermore, after a few hours, when the control voltage has been restored to the initial value of 0.38V, the T of the heater does not return to the initial value (ie 156C), but remains a lower value (ie 148C). This raises suspicions more on the temperature sensing than on te heating system.
In the afternoon we started to do a test using another acquisition channel (at level of the IMMS box) for the TE_IntHeater sensor , and then at 17:14 UTC increased the Vdac to 0.42V for a short time, but the strange behavior happened again. Tomorrow we will proceed to replace the front-end electronics of the temperature sensor and check the behavior again.
This morning we tried to replicate the CHRoCC strange behavior observed yesterday. The command voltage sent with DAC (CHROCC_V_DAC channel) was incresed from 0.7V to 0.74V.
The initial heater temperature was 229°C (TE_IntHeater channel).
At the first trial (started at 9:18 UTC), the V_IN signal (the command voltage sent to KERT power supply), has been removed from DAQ ADCs and acquired with an external system.
The reflector temperature increases an decreases as expected without stange behaviors.
At the second trial (started at 10:03 UTC), when we connected also the DAQ ADC to acquire V_IN signal, again we didn't observe any strange behavior.
Setting V_DAC to the initial value (0.7V), the IntHeater temperature returns very close to the initial value.
A further test could be performed with V_DAC set to 0.38V.
Yesterday, we investigated again the CHRoCC strange behavior observed during the test of January, 15th, when an increase of Vdac, caused an initial negative transient of the IntHeater temperature.
During the new test, we were not able to reproduce the anomaly. The IntHeater temperature, increases and decreases with Vdac, as expected without opposite sign transients.
