Tachogenerators

tachogenerator is a device which generates an electrical output directly proportional to the shaft speed. The voltage thus generated is fed to a speedometer for speed measurement and/or used as feed - back signal for controlling the speed of a rotating machine / equipment. In every automatic control system, since the system performance is directly related to the performance it becomes essential that the tachogenerator must satisfy certain minimum requirements such as:
linear
the rectified output voltage should be strictly linear with respect to the rotational speed 
output signal 
the ripple content in the rectified output signal must be as low as possible 
temperature effect 
variations in ambient temperature should have negligible effect on the tg output
long-term stability 
instability of output cause due to aging of parts, shift in magnetic circuits etc., should be minimum.
unique features of tachogenerator
• alinco permanent magnet in the rotor assembly gives long term stable
  operation under varying ambient temperature.
• large number of poles (48) results in a high frequency output and hence
  good dynamic response, linearity and wide speed control,   along with low
  ripple content in the rectified output.
• rotor and stator assemblies are encapsulated with epoxy resin to prevent
  any ingress of moistures, dust etc.
• ac tachogenerators in 24 or 48 pole constructions with quasi-sinusoidal
  output of 30/ 50 volts ac (rms) @ 1500 rpm
• stator assembly is housed in cast iron body to minimize magnetic 
  interaction and consequent losses.
• grease filled, double shielded ball bearings are used for maintenance free
  operation.
• two mounting options-foot mounted and flange mounted.
• speedometer can be calibrated to suit the customer's requirements.
• compact and rugged construction provides longer life with excellent
  performance even under severe environments.
• if required, tg can be supplied with rectifier unit, for dc operations.
• technical specifications
• type -totally enclosed
• class of insulation -b
• voltage -30v / 50v ac and frequency 600hz at 1500 rpm
• max. Load resistance at output - 600 ω
• no. Of poles - 48 
• linearity - 0.5%