Using an analog temperature sensor near 3-phase 150V , 40A Motor Controller?
The datasheet gives some strong advice on decoupling.


  Note the 0.1 µF bypass capacitor on the input. This capacitor
  should be a ceramic type, have very short leads (surface-mount
  is preferable), and be located as close as possible in physical
  proximity to the temperature sensor supply pin. Because these
  temperature sensors operate on very little supply current and
  may be exposed to very hostile electrical environments, it is
  important to minimize the effects of radio frequency interference
  (RFI) on these devices. The effect of RFI on these temperature
  sensors specifically and on analog ICs in general is manifested as
  abnormal dc shifts in the output voltage due to the rectification
  of the high frequency ambient noise by the IC. When the
  devices are operated in the presence of high frequency radiated
  or conducted noise, a large value tantalum capacitor (±2.2 µF)
  placed across the 0.1 µF ceramic capacitor may offer additional
  noise immunity.


Did you comply?

The datasheet continues ...




  Figure 32 illustrates a way to convert the output voltage of a
  TMP35/TMP36/TMP37 sensor into a current to be transmitted
  down a long twisted pair shielded cable to a ground referenced
  receiver. The temperature sensors are not capable of high output
  current operation; thus, a standard PNP transistor is used to
  boost the output current drive of the circuit. As shown in the
  table in Figure 32, the values of R2 and R3 were chosen to
  produce an arbitrary full-scale output current of 2 mA. Lower
  values for the full-scale current are not recommended. The
  minimum-scale output current produced by the circuit could be
  contaminated by ambient magnetic fields operating in the near
  vicinity of the circuit/cable pair. Because the circuit uses an
  external transistor, the minimum recommended operating
  voltage for this circuit is 5 V. To minimize the effects of EMI (or
  RFI), both the circuit and the temperature sensor supply pins
  are bypassed with good quality ceramic capacitors.


See also the 4-20 mA section.