There are three common display arrangements found in microwave instruments used within the UK.
a) This arrangement is usually moving coil meter with a linear or modified response, the quality of which is determined by the price of the instrument. Some technicians prefer this form of display as they feel it is easier to determine the average value of a varying signal. However, as with all displays of this type, they do not respond well to shock and there is always the possibility of parallax error when reading.
b) The display in this case is commonly LCD with the option of a back-light for greater contrast. The importance of achieving the correct signal averaging cannot be overstated. However, when this is accomplished the advantage of a direct unambiguous reading is not to be overlooked. With no moving parts and well positioned they are perhaps more resilient to shock than their analogue counterpart.
They also offer the option of including additional information within the display at little extra cost. e.g. low battery indication, overload condition etc.
c) There are a number of instruments available within the UK in which LEDs form the display arrangement. The LEDs are arranged to illuminate if the instrument detects a signal above a given level. Although simple in concept, difficulty arises when attempts are made to calibrate as unlike options (a) and (b) no truly accurate indication is available on the instrument to show how much above or below the nominal setting the signal is before the LED illuminates.
Options (a) and (b) offer the prospect of resolution at 0.1mW, although in the case of (a) the cost rises whereas (b) provides a cost effect arrangement. The resolution in option (c) is not relatively coarse. Owing to the nature of the display arrangement.