Fisher 846 - In-Service Troubleshooting

Instruction Manual
D102005X012
846 Transducer
June 2017
26
1) Find frequencies at zero and span pressure.
2) Solve for m, using equation (2).
3) Solve for b by inserting m, initial pressure,
and initial frequency into equation (1).
4) Insert m and b into equation (1) to find conversion formula.
Procedure
(1) P = m(p) + b
P = pressure
p = frequency
(2) m =
P
2
- P
1
p
2
- p
1
Equations
Example
1)
2)
3)
4)
P
1
= 3 psig
p
1
= 6000 Hz
P
2
= 15 psig p
2
= 9000 Hz
m = =
15 - 3 12
9000-6000 3000
3 = (6000) + b
12
3000
b = 3-24
b = -21
P = (p) - 21
12
3000
Figure 13. Wiring Connections for Frequency Counter
CONTROLLER
POWER
SUPPLY
FREQUENCY
COUNTER
TEST
PINS
POSITIVE
NEGATIVE
GROUND
B2466
In‐service Troubleshooting
A number of simple checks can be made on the transducer while the unit is in service. Figure 14 shows a
troubleshooting flowchart.
1. Make sure that the module cover is tight. The cover should be hand‐tightened and then advanced 1/4 to 1/2 turn
(24 to 27 NSm) (18 to 20 lbfSft).
2. Confirm the general functionality of the unit by using the diagnostic features described earlier in this section.