Original:

if {1} {	# Setting up the Primary Voltage1
	grid [ttk::labelframe .nb.classic.inputvoltage1 -text "Primary Voltage 1" ]
	pack [ ttk::entry .nb.classic.inputvoltage1.entry -width 15 -textvariable input_voltage1] -side right -fill x;
}

Neu:
					# hbs_global_com_open = Flag für COM Port geöffnet und verbunden
if {hbs_global_com_open == 1} {		# Setting up the Primary Voltage1 if COM Port is open
	grid [ttk::labelframe .nb.classic.inputvoltage1 -text "Primary Voltage 1" ]
	pack [ ttk::entry .nb.classic.inputvoltage1.entry -width 15 -textvariable input_voltage1] -side right -fill x;
}