You can’t evaluate a greater than or less than in a switch function. A workaround as per this thread is to use binEnum like this:
switch(
binEnum({Brac Tags/Analog_In/PET_150}=1,
{Brac Tags/Analog_In/PET_150}>50,
{Brac Tags/Analog_In/PET_150}<25),
1,2,3,
'color(217,0,0)', //result 1
'color(217,217,0)', //result 2
'color(0,0,0)', //result 3
'none') //default
The manual page for Switch is here.