procedure TForm1.FormCreate(Sender: TObject);
begin
  edtCtrlThd1.EditType:= etFloat;
  edtCtrlThd1.MaxFloatValue:= 999.99;
  edtCtrlThd1.MinFloatValue:= -999.99;
  edtCtrlThd1.Signed:= true;
  edtCtrlThd1.MaxLength:= 7;
end;

procedure TForm1.edtCtrlThd1Exit(Sender: TObject);
var
  f:Double;
begin
    f:= StrToFloat( TAdvEdit(sender).Text);
  if f>TAdvEdit(sender).MaxFloatValue then
    TAdvEdit(sender).Value:=TAdvEdit(sender).MaxFloatValue
  else
  if f<TAdvEdit(sender).MinFloatValue then
    TAdvEdit(sender).Value:=TAdvEdit(sender).MinFloatValue ;
end;