Subroutine:   irus_inst
 
Purpose:      obtain a instrument name from the user
 
File:         irus_inst.sh
 
Author:       Do Kester
 
Person resp.: Do Kester
 
Address:      guspace!do or rugfx4!do         (uucp)
 
Use:   call irus_inst(
		default	    	I	integer
 		instrname ) 	I/O	character*(*)

  default 	default level as in USERxxx
  instrname	instrument name

Description:
  The keyword INSTRUME is posed to the user until a valid IRAS instrument
  has been selected.

  	INSTRUME=	Valid IRAS instrument name: A combination of
			observation mode and band number
  Valid observatio modes are ( 2 letters suffice )
	SURVEY	SPLINE	AO	FLASH  UNKNOWN
  Valid band numbers are ( 2 letters suffice )
	12 25 60 100 LRS BPHF 1 2 3 4 B1 B2 B3 B4
  ( They are searched in this order! )

  When the user chooses the default, INSTRNAME is returned unchanged.
 
Externals:    IRCC_BANDNR IRCC_OBSMODE IRCC_INSTRNAME
 		ANYOUT CANCEL
Updates:      5 jun 1990 DK, documentation only
		7 sep 1990 DK, code