Chapter 2
SQM-242 CoDep
2-9
Analog:
The SAM-242 analog input card measures DC voltages in the +/-10 volt range.
These voltages may represent temperature, flow, or any other process variable. The
analog frame allows you to modify the display to show values in the desired units, using
a linear (y = mx + b) transformation.
Assume you have a temperature transmitter that sends 0V at 0
°
C and 10V at 100
°
C.
You want to control temperature to 200
°
F (it’s an example!). Set the analog input Gain
to 18, Offset to 32, and Units to Deg F (F = 9/5C + 32). The SQM-242 will display
setpoints and measurements associated with the analog input in degrees F.
To leave the analog input display in Volts, set Gain = 1 and Offset = 0.
Gain:
The gain term for transforming voltage to measured units. This is the m term in
y = mx + b.
Offset:
The offset term for transforming voltage to measured units. This is the b term in
y = mx + b.
Units:
The units that you wish to display for the analog input.
Monitor:
An analog input can also act as a monitor to stop deposition. For example, an
analog signal from an optical monitor could stop deposition when a certain voltage is
reached. A voltage input from a pressure transducer might also prevent deposition until
a certain vacuum is reached.
Setpoint:
The voltage measured by a monitor input that will halt deposition. Analog
setpoints are entered in Volts, not calculated units!