A 12 channels system is as you're saying a three scopes system solution.
An possible approach can be to trigger the first scope on one of the signals and then make use of the Trigger Out capability to daisy chain the scopes. Using such a set up helps to make sure all scopes trigger on the same event whereas using external trigger carries the risk to trigger the scopes on different events. In the case of external trigger to the three scopes one has to be very careful with synchronizing multiple scopes.
We focus now on te daisy chain solution and give a description about the configuration of the system.
Signal Source: LW120
Waveform: Square Wave; Rise Time approx. 10ns
Frequency: 50 Hz
LW120 C1 -> Master, C1
LW120 C2 -> Power Split into Slave C1 and Slave2 C1
Description:
Chanel 1 of the LW120 is connected to C1 of the Master scope, an LT262. This scope has the Rear Out set to Trigger Out which is connected to External Trigger of the scope Slave 1, an LT374. Again the Rear Out is set to Trigger Out and connected to Slave 2, an LT344.
This configuration allows to trigger with the master scope the other two scopes in this kind of daisy chain configuration.
Below we qualify now the time delay we introducce in the system because of this chain and the trigger jitter of the scopes slave 1&2.
See attachments:
1. Master LT262 Trigger C1; Trigger Out;
2. Master Panel Setup
3. Slave 1 LT374; Trigger Ext on Trigger out of Master
4. Slave 1 Panel setup
5. Slave 2 LT344; Trigger Ext on Trigger out of Slave1
6. Slave 2 Panel Setup
The delay is around 36ns of Slave 1 and then 74ns of Slave 2. This is expected because it is a daisy chain and we add another scope in the chain. On the other hand, the experiment proves that the trigger jitter stays about the same for the second scope whereas the range is compareable and the sigma is slightly higher.
In this proposal the scopes use internal sample clock.