Pump drive torque measurement problem

[daveydude_99]

Hi all!

Basically I will soon be required to measure the torque required to drive a plunger pump which operates by an eccentric cam on the pump's driveshaft pushing a plunger up and down. So obviously the torque will vary through the driveshaft's revolution.
The setup is as follows: Motor - couplings - torque transducer - couplings - pump.
The problem I have is that the couplings are fairly heavy and obviously themselves require torque to be driven round with the pump, and the information I want is the PUMP's drive torque, not the pump plus couplings. The couplings are all symettrical so their drive torque shouldn't vary through the revolution of the driveshaft, and the transducer doesn't offer too much resistance. I have or can obtain the rotational inertia for each coupling, I am just wondering how I translate this inertia into a resistive torque so I can subtract this number from the torque readings I obtain. The torque will be measured at a set of constant rotational velocities.

Any help that I receive will be greatly appreciated.

Regards,

David

 

[Baluncore]

If the motor runs at a fixed speed then the couplings will not be changing speed and so there will be no torque needed to cyclically accelerate and decelerate them. Only when there is some rotational slack in the couplings will a cyclic torque be required to rotate the couplings.