Badger Meter Vortex Meters - Manual (Page 9)

Form No. 09-VRX-UM-00007 7
BACK PRESSURE
Back pressure (the pressure immediately downstream of the meter) must be maintained above a mini-
mum level in order to avoid cavitation. For most applications, this may be ignored if the flow rate is less
than 75% of maximum. For other liquids, use the following formula to calculate the minimum back pres-
sure.
Back Pressure = 2.75 ΔP + 1.25 PV - 14.7
Where:
Δ P = Pressure drop in psi at max flow
PV = Vapor pressure in psia of the liquid at operating temp.
(eg. the PV of water at 100 °F is 0.42.)
BP = Back pressure (downstream of meter) in psig.
As an example, for water, at 100 °F (37 °C) in a ½” meter, where the maximum pressure drop is 8 psi mini-
mum back pressure is 7.8 psig.
BP = (2.75 Ч 8) + (1.25 Ч 0.42) - 14.7
BP = 22 + 0.525 - 14.7
BP = 7.825
TEMPERATURE
To protect the internal crystals in each unit, temperature limitations must be adhered to. All permissible
operating temperatures are identified by meter and material type. Additionally fluid temperature will af-
fect maximum working pressures. For de-rating information see the maximum fluid operating pressures
for the specific flow meter model.
OUTPUTS
The RVL series meters can be obtained with either an analog output or a rate frequency output. The
standard analog output is a 4-20 mA current an optional 0-5 VDC is also available. The analog output can
also be re-configured in the field using a PC communications cable and programming software which
are both available from Racine Vortex as P.N. RVS220-954.
The analog current output varies between 4 mA (0 flow) and 20 mA
(maximum flow). The 0 to 5 VDC analog output is also continuously
variable between 0 V (0 flow) and 5 V (maximum flow).
NOTE: One of the two analog output options (4-20 mA or 0-5 VDC) are hard-
ware selected at the factory and can not be changed in the field.
The rate frequency output produces pulses whose frequency is
proportional to the flow going through the meter. Each meter has a
slightly different output frequency which is listed on the calibration
sheet that accompanies the meter. Table 2 shows the long term aver-
age full scale output frequency for standard size meters.
Meter Size
in (mm)
Average Full Scale
Frequency (Hz)
Pulse Width
(msec)
¼ (6.4) 1055 0.47
½ (12.7) 820 0.61
½ (12.7) 570 0.88
¾ (19.1) 284 1.76
1 (25.4) 292 1.71
1½ (38.1) 144 3.47
2 (50.8) 148 3.38
3 (76.2) 61 8.20
TABLE 2