Spectrum Controls 1771sc-IFE32 - Manual (Page 34)

24 PLC-5 TM 32-Channel Analog Input Module
set to zero (default), no user scaling is performed.
The slope line represented the module response may be defined from any two points
on the line defined as (X0, Y0) and (X1, Y1). The X axis is assumed to be the scaled
data value and the Y axis is the ADC output representing the channel input. The
following is an example:
Y= voltage
+10V
X = scale value
Y = mX + B
Y = value at Y axis
X = value at X axis
B = Y intercept when X = 0.
M = slope of line = (Y1 – Y0)/(X1 – X0)
Range: -10 to +10 Volts
Min Scale: -1000
Max Scale: +1000
X0 = -1000 (min scale)
Y0 = -10V (min range)
X1 = +1000 (max scale)
Y1 = +10V (max range)
M = (10 – (-10))/(1000 – (-1000)) = 2000/20 = 0.01
B = Y – mX = 10 – (0.01 * 1000) = 10 – 10 = 0
If Y = 10 X = (Y – B)/m = ((10) – 0)/0.01 = 1000
Channel Voltage: Scaled Input Data:
-10V -1000
-5V -500
0V 0
+5V +500
+10V +1000
Scale values are defined using the same format as selected for their respective
channels. If a channel group is configured for the BCD format, the scale values must
be specified in BCD. If the group is configured for a binary format, the scale values
must be specified in binary form.
Scale values may be defined using bipolar limits (e.g. -1000 to +1000) or unipolar limits
(e.g. 0 to 1000) regardless of the input range specified.
If the signed 12 bit binary or signed BCD formats are selected, the min_scale/
max_scale values require special handling for negative values. The value to be
entered in this case is abs(scale_value)+8000hex.
For example, if min_scale = -1000 and max_scale = 1000 and format is signed BCD:
min_scale = -1000
BCD
= (abs(-1000
BCD
)) + 8000
16
= 1000
16
+ 8000
16
= 9000
16