Peak and Valley

Outputs Y28 and Y29 are used to reset the valley or peak hold functions.

Hold Reset

The operation during reset is dependent on whether the hold function is

 

enabled for each individual channel.

 

Figure 3-15 shows how the peak value and the valley value react during

 

reset.

 

 

 

 

Peak or Valley Hold Function

 

Enabled

Reset to current input value

 

Disabled

Reset to zero

 

 

 

 

Figure 3-15 Peak/Valley Reset Truth Table

Flag Bits

When not using peak or valley hold, WX49 ± WX54 return flag bits for each

 

of the functions, and each of the channels may be interrogated with ladder

 

logic instructions.

 

The flag bits correspond to the 16 channels in the module. The LSB or bit 16

 

corresponds to channel 1, and the MSB or bit 1 corresponds to channel 16.

 

See Figure 3-16.

Bit #

MSB

 

 

 

 

 

 

 

 

 

 

 

 

 

 

LSB

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

1

 

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Channel # 16 15 14 13 12 11 10 9 8 7 6 5 4 3

2 1

Figure 3-16 Mapping Bit Position to Channel Number

Alarm flags (WX49) The alarm flag bit is the logical OR of the low alarm bit (WX5) and the high alarm bit (WX50) for each channel. This allows one simple check to determine if an alarm exists on a channel. These alarm bits reset automatically when the alarm condition is no longer true. In the event that an alarm exists on a channel, the ladder logic may determine whether the alarm has reached the low alarm or the high alarm.

SIMATIC 505±2557 Installation and Operation Guide

Advanced Function Programming 3-23

Page 53
Image 53
Siemens 505-2557 installation and operation guide Hold Reset, Flag Bits