Example: Engineering Units

The Analog Threshold Control example reads raw counts and scales them to volts in the program. Switching the module’s Reading Format to Engineering Units moves that conversion into the HAL: the channel appears directly as a REAL in the engineering unit of the module (volts, milliamps, degrees).

Hardware

Slot	Module
1	SLM-AI-8-V (8-channel 0-10 V analog input)
2	SLM-DCO-15P (15-channel sourcing DC output)

Same wiring as the base example.

Backplane configuration

Add both modules in order. Set the analog module’s Reading Format to Engineering Units.

With Engineering Units selected, the analog channel occupies a %ID location (double-word real) rather than %IW (word integer):

Slot	Channel	Address	Alias
1	AI1	%ID0	Level_Volts
2	DO1	%QX0.0	Bar_1
2	DO2	%QX0.1	Bar_2
2	DO3	%QX0.2	Bar_3
2	DO4	%QX0.3	Bar_4

The program

Variables

The level_raw row from the base example is gone, replaced by level_volts mapped directly to the input.

Variables table

Name	Class	Type	Location	Initial Value	Documentation
level_volts	Local	REAL	Level_Volts		0.0 - 10.0 V directly
bar_1	Local	BOOL	Bar_1		First lamp
bar_2	Local	BOOL	Bar_2		Second lamp
bar_3	Local	BOOL	Bar_3		Third lamp
bar_4	Local	BOOL	Bar_4		Fourth lamp
segments	Local	INT			How many lamps should be lit

Text mode

  VAR
    level_volts : REAL AT Level_Volts; (* 0.0 - 10.0 V directly *)
    bar_1 : BOOL AT Bar_1; (* First lamp *)
    bar_2 : BOOL AT Bar_2; (* Second lamp *)
    bar_3 : BOOL AT Bar_3; (* Third lamp *)
    bar_4 : BOOL AT Bar_4; (* Fourth lamp *)
    segments : INT; (* How many lamps should be lit *)
  END_VAR

Code body

IF    level_volts >= 7.9 THEN segments := 4;
ELSIF level_volts >= 6.0 THEN segments := 3;
ELSIF level_volts >= 4.0 THEN segments := 2;
ELSIF level_volts >= 2.0 THEN segments := 1;
ELSE                          segments := 0;
END_IF;

bar_1 := segments >= 1;
bar_2 := segments >= 2;
bar_3 := segments >= 3;
bar_4 := segments >= 4;

The code is identical to the base example apart from the removed scaling line.