5.2 DIGITAL INPUT
LogBox 3
G
has a di
gital input channel that can be configured for "Pulse Count", "Event Logging" or even "Log Control" modes. The digital input
can be disabled.
Regardless of the fu
nction for which it will be used, the type of sensor that will be connected to the input must be configured: PNP, NPN or Dry
Contact (see
Installat
ion
chapter to see how the sensors s
hould be connected). Moreover, the edge of interest for the digital signal needs to be
selected to generate the count, event or logging start/end: rising edge, falling edge or both edges.
Relationship between Sensor Typ
e, Sensor Status and Logical Level obtained in LogBox 3G
Sensor Type
PNP
NPN
Dr
y Contact
Sensor Status
Open
Closed
Open
Closed
Open
Closed
Table 04
- Digital Input
Logical Level
0
1
1
0
1
0
For Dry Contact sens
ors, a debounce time of at least 50 ms needs to be configured (sensor stabilization time/time during which the sensor should
remain in the appropriate status for it to be considered vali
d). Debounce time does not need to be configured for PNP or NPN sensors in "Pulse
Count" mode. However, if the digital input is configured for the
"Event Logging" or "Log Control" modes, a minimum debounce of 50 ms is required
to keep any noise fro
m generating a false event. In the "Event Logging" and "Log Control" modes, events will be generated after the end of the
debounce time.
5.2.1 PULSE COUNT
When setting the digit
al input in "Pulse Count" mode, you can select an application mode: "Flow Rate" or "Count".
The "Flow Rate" mode allows, if "Average Flow by Acquisition Interval
" is selected, to log the average flow rate or, if "Volume Since Last Reset" is
selected, to count the total volume within a previously configured period until the count is reset.
The "Count" mode, in turn, allows, if the "Acquisition Interv
al Counting" option is selected, to count the number of pulses that occurred within the
Log Interval or, if the "Accumulated Count Since Last Reset
" , to count the total number of pulses logged within a preset period until the count is
re
set.
LogBox 3
G
has a 32-bit register, responsible for accumul
ating the volume or number of pulses within a certain configurable reset interval. For
example, you can s
et the device to reset on a monthly basis or on a specific day and time (see the
Accumulator Resetting
sectio
n of the
Configuration Software
chapter).
LogBox 3
G
also ha
s a 16-bit register, responsible for measuring the average flow rate per acquisition interval or for performing the count per
acquisition interval. At each logging interval,
LogBox 3G
co
unts the number of pulses that have occurred and registers it in memory, resetting the
register so that it can accumulate the pulses of the next interval.
If
the sensor is a Dry Contact type, the
LogBox 3G
count registers (16 bits and 32 bits) will be able to count up to 10 pulses per second. For PNP
and NPN sensors, 2
000 pulses per second. However, in the case of the 16-bit register, it is important to note that these pulses will accumulate
wi
thin each logging interval. Thus, if the "Average Flow Through Acquisition Interval" or "Acquisition Interval Count" modes are selected, it is
necessary to evaluat
e the maximum sensor frequency so that it does not exceed 65535 counts (16 bits) within the logging interval, causing an
overflow in the logger that accumulates them.
If
the maximum sensor frequency is 2 kHz,
LogBox 3G
will accumulate 2000 pulses per second for up to 32 seconds. Upon exceeding this interval,
the number of accum
ulated pulses will exceed 65535 counts, resulting in overflow in the 16-bit register. For a sensor that can reach 2000 pulses
per second, the reco
mmended log frequency should be less than 32 seconds.
When the option "Vol
ume since last reset" or the option "Accumulated count since last reset" is selected, the number of counts is, in turn, limited by
the 32-bit accumulator register and, thus, enables the counting of a limit number of 4294967295 pulses. Thus, the periodicity of the reset must also
be adjusted according to the frequency of the sensor pulses
. By keeping the same example of sensor use at maximum frequency, i.e. 2 kHz, it is
recommended that th
e periodicity be less than 24 days, otherwise an overflow will be generated in the register.
In typical applications, such as flow and volume measurement
, simple pulse counting is not enough, and these pulses need to be converted into a flow
unit. To do so, the desired flow unit and a conversion factor c
an be selected to transform the number of pulses generated by the connected transmitter
into flow information. Pulses logged in the interval will be conv
erted to the user-configured flow unit every time the logged data is displayed.
To facilitate configuration of the digital channel in "Pulse Count
" mode and conversion to the flow unit required,
LogBox 3G
provides the following
measurement units:
Flow Units
l/s,
l/min,
l/h,
gal/s,
gal/min,
gal/h,
m³/s,
m³/min,
m³/h.
Sensor Units
pulses/l,
pulses/gal,
pulses/m³.
Table 05
– Measurement Units
19/66
