Multi-Tech Systems 7600, 7500 manual Considerations when scaling, 20 to, To 20 mA

Setting Analog Zero and Full Scale Values ION 7500 / ION 7600 User’s Guide

Considerations when scaling

1.Set the Full Scale value that you expect. For example, consider scaling an Analog Output module whose Source input is linked to kW values; if the highest Watt value that you expect is 10 kW enter 10,000 as the Full Scale value.

2.Consider the output type you have, (-1 to 1 mA, -20 to 20 mA, 0 to 20 mA) and then consider the output range you want (0 to 1 mA, 0 to 20 mA or 4 to 20 mA). For example, the Analog output on an I/O Expander may be 0 to 20 mA, and the analog device connected to the I/O Expander may support a range of 4 to 20 mA.

3.Calculate the Zero Scale setting according to the table below. The table assumes the Source input varies between Zero Scale and the Full Scale settings.

Output Type	Desired Range	Zero Scale Setting*	Full Scale
			Setting
-1 to 1 mA	0 to 1 mA	negative value of Full Scale (e.g. -1000)	e.g. 1000
-20 to	0 to 20 mA	negative value of Full Scale (e.g. -1000)	e.g. 1000
20 mA	4 to 20 mA	-1.5 times value of Full Scale (e.g. -	e.g. 1000
		1500)
0 to 20 mA	4 to 20 mA	-0.25 times value of Full Scale (e.g. -	e.g. 1000
		250)

*To determine the Zero Scale multiplier, calculate the ratio of minimum desired output to the desired range:

ZeroScaleMultiplier =	MinimumDesiredOutput
	MaximumDesiredOutput------------------------------------------------------------------------------------------------------------------------------------------– MinimumDesiredOutput

For example, assume output type is 0 to 20 mA and desired range is 4 to 20 mA:

0.25 =	4mA
	20mA---------------------------------– 4mA

NOTE

The Zero Scale setting is minus 0.25 times the Full Scale value as explained in the following section “Determining the Zero Scale setting for output ranges below zero”. Although the section describes setting for ranges below zero, the calculation proves the multiplier is negative for output ranges starting at zero.

Page 228 Digital and Analog I/O Technical Note