Max Machinery 286-300 SERIES TRANSMITTERS - Manual (Page 9)

Rotational Speed of Piston Meter Crankshaft At Constant Flow
0 90 180 270 360 450 540 630 720
Crankshaft Angle
Cr
a
n
ksh
a
ft
Ro
ta
tio
n
a
l
S
p
e
e
d
Calibration
The coils of the Model 286 stator, the printed circuit board, and the flow meter need to be calibrated as
one set. When used with any flow meter model, the calibration procedure initiates a routine that
determines the offsets needed to balance the output signals from all of the coils. When used with a 210
series piston flow meter, the calibration procedure includes an additional routine that measures the
angular position of the stator with respect to the meter. This allows the transmitter to compensate for
cyclical variations in rotational velocity of the meter, resulting in a steady output frequency. When S4-
1 is in the 210 position (piston meter), the calibration will automatically include both of the routines
described above. If S4-1 is in the 220/240 position (Gear or Helix Meter), only the coil balancing
routine will be performed.
The recommended flow range for calibration is that which will turn the meter at 20-500 rpm. Lower
flow rates (resulting in rotor speeds below 20 RPM) will cause the ‘SLOW’ LED to come on and the
calibration will not take place. Successful calibration will occur at higher flow rates (rotor speeds above
500 RPM) but the results may not be as good as those which would be obtained at a lower flow rate. A
flow rate resulting in a flow meter rotor velocity of 100 rpm will give good calibration results.
When doing a calibration on a piston meter, it is critical that the flow rate remains constant (less than
10% variation) for the routine that determines the stator angle to be successful. When a steady flow
passes through a four-piston meter, the crankshaft speeds up and slows down 4 times per revolution.
The phase of this cyclic speed variation is determined during calibration by finding the position of the 4
speed peaks in a revolution. These speed peak locations are measured for 8 revolutions (32 peaks), then
run through an averaging procedure. Once this is done, the tachometer can internally compensate for the
speed variations to output a steady frequency under steady flow conditions.
Error can be introduced into this phasing procedure if the system flow rate is pulsating (i.e.: driven by a
piston pump). If there are peaks in the flow rate that overshadow the speed peaks due to the 4-piston
geometry, the calibration routine will incorrectly determine the phase of the cyclic speed variation and
will subsequently apply the compensation out of phase.
286-300-350 © 2002, Max Machinery, Inc.
Calibration
(9)
Discontinued