When should one migrate from analog to isolated digital control
The Licel APD detectors are susceptible for analog interference form the laser source due to their high internal amplification (20000 times). The analog remote control of the APD adds another ground path which might then be exploited by the laser noise to enter the system. Usually this is best seen when taking a dark measurement. One expects a flat baseline. If there are waves on the baseline which go away when one disconnects at the rear the remote cable. Then the following procedure has a significant chance of improving the situation.
The digital control is shipped in remote controlled systems since early 2023. It has a galvanically isolated digital control which cuts the above described ground loops.
We retrofitted this also into old cassettes, so that instead of buying new APD cassettes one can upgrade existing APD cassettes to the digital interface and change the Ethernet controller from APD-Remote-4 to APD-Remote-Dig.
Please contact Licel, if you think that such an update would improve your system. Please provide a dark measurement file:
- with remote control and
- one file where the remote control cable has been removed (Please notice that switching at the front panel of the cassette from remote to manual is not enough, you need to take the cassette out and to remove the cable
Warsaw 2023
There should be a clearly visible change as shown above.
Step 1 - Rack identification
before changing the system we need to document the internal values so that they can be restored if something goes wrong.
Please follow the rack identification procedure and run the Inspect System.exe on the system and provide the information to Licel.
Step 2 - APD Cassette identification
Look at the cassette from the front. If it has the small TEC LED near
to the switch , this is the latest version and no upgrade is needed.
We refer to this as the PCB digital control variant.
If the LED is not as mentioned above see the rear. If the connector at the rear looks like below you have already a modified cassette and the upgrade has partially been done. An upgrade to the latest version should be done, as the new cassettes outperform the intermediate states. These are intermediate digital control variants.
If the connector looks like the image below, the upgrade is possible but it would also require a change of the remote control and the remote cable. Please provide the serial number of the cassette and the system information to Licel. We call this the analog control variant.
Each cassette has a serial identification
Please provide this number together with the systeminfo from above to Licel.
Step 3 - Order process
With this information Licel can provide you a quote for the upgrade and ensure that all material is in stock before you ship the rack to Licel.
We need the rack with the APD cassettes mounted without detectors and cables.
Please estimate that it will take one week from your shipping of the rack till you get it back.
If more than one rack needs to be changed a mixed procedure with sending the cassettes for modification to Licel and then an on site change of the Ethernet controller might be a better but slower choice.
Detector head update
In 2025 we changed the detector head pcb and got a significant reduction in baseline noise.
Existing heads can be upgraded with this modification. This modification
relies on the APD isolated remote control described above
Costs
| Item | Costs |
|---|---|
| Changing the Ethernet remote control from Analog to digital | 420 Euro |
| New remote cable | 80 Euro |
| New APD cassette | 2400 Euro |
| Upgrading an existing cassette | 800 Euro |
| Upgrading the detector head | 1500 Euro |