PTZ-BOX 5.0 User manual, document edition: 13
30
6.1.3
Reverse flow support
The purpose of this functionality is to ensure conformity of the gas meter counter with a dedicated
device counter (
Vm
or
V2
and auxiliary
Vo
) in case of reverse flow situations.
•
There are 2 configurations of pulse inputs dedicated to detecting reverse flow from the
internal encoder module: D-LF1/LF2 and D-HF1/LF2; A phase shifted signal between two
inputs is required.
•
In configurations D-LF1/LF2 and D-HF1/LF2, the internal encoder module receives two
LF1/LF2 input signals (HF1/HF2) and outputs the processed relative LFs (HFs) counter. This
LFs (HFs) counter will increase or decrease depending on the detected flow direction. The
auxiliary inputs (
LF2
,
HF2
) operate only in one direction (they can only grow independently of
the direction of flow).
•
Failure to detect the sequence (phase shift) results in the lack of volume counting to the
Vm
counter - it is possible in the case of e.g. damage to one of the pulse circuits.
•
Detection of reverse flow results in immediate resetting of
Qm
flow.
•
The reverse counter
VmR
and the reverse increment
dVmR
are driven only when the reverse
count is detected on the main counting path, i.e. on the
Vm
counter (i.e. in 8 configurations:
SCR, SCR/LF1, SCR/HF1, EN, EN/LF1, EN/HF1, D-LF1/LF2, D-HF1/LF2). In other configurations,
any gas reversal will be visible only on the
V2
counter.
•
The
Vm
counter (or
V2
and auxiliary
Vo
) can increase and decrease - to track the counter of
the gas meter. Size of reverse flow is represented by the
dVmR
increment and the
VmR
counter.
•
The
Vb
counter (similarly
E
,
M
and their emergency versions) is frozen during the reverse
flow. Operation is resumed when the volume
Vm
measured in the reverse direction is
balanced with the appropriate amount of volume in the forward direction.
•
The
V2
counter is driven from the control input - it always increases (unless it comes from
the encoder input enabling reverse flow). When the reverse flow occurs, this will cause
permanent non-compliance of the
Vm
and
V2
counters. Unless the user manually resets the
counters, there will be compliance:
V2
=
Vm
+
VmR
.
•
When the main counting input is an encoder (NAMUR or SCR) - the
Vm
will react to the
forward and reverse drive according to the read out meter of the
Vo
encoder (e.g. SCR/LF).
Then, the control counter
V2
will be driven from a conventional (impulse) source, so that
each subsequent pulse will increase the value of this counter (e.g. when the gas is reversed,
the encoder will give a reverse signal by reducing the counter, but the LF pulse can be
generated and drives the counter
V2
forward).
•
After the reverse flow is detected, a
Reverse flow
alarm will be generated. This alarm will be
closed when
dVmR
reaches 0.
6.1.4
Digital inputs
PTZ-BOX 5.0 is equipped with up to 8 binary inputs, which may
–
according to chosen configuration
of counting inputs
–
work as digital (signaling) inputs. These inputs are intrinsically safe. Inputs
DI1..DI5 and DI8 are adapted to work with potential-free reed contacts. Inputs DI6 and DI7 are
adapted to work with inductive NAMUR transmitters. When active state is detected on digital input,
appropriate event will be stored in device’s memory.
Device allows to change name of digital input, which will be used during record of event.
Modification of name is possible by editing parameters
DI1Desc
÷
DI8Desc
.
