Tip of the Day 125: Always Ground Temperature Modules

We have discovered from time to time that customers find noise on their cavity temperature sensor signals. As noted in the install document it is critical that, when using a grounded thermocouple (as our TS-PF03-K sensor) the electronics that measure that sensor must be grounded to the same steel that the sensor is. In other words, the Lynx Quad Temperature module LQT should be bolted to the mold. If it cannot be bolted to the mold (as in hot molds) it must be grounded to the mold somehow. Some molds have insulating plates between clamp plate and platen. We cannot always depend on case-hardened clamps being a good ground.

When the LQT is not grounded you can get the kind of noise shown below. The eDART uses a 2° rise to detect the flow front arrival (for Process Time / Temp @… and for controls). Thus the noise with the LQT un-grounded completely confuses the eDART’s ability to interpret the signal.

Additional Points re: Shielding

  • Thermocouple wires must also be shielded. The mold makes a shield if they remain buried all the way up into the LQT. If not then they need slip-on shield.

  • A „step“ on the LQT (one digital value to the next) is 0.1 °F of temperature change. The electrical signal from the thermocouple for 0.1 °F  is only about 2 millionths of a volt (0.000002 volts, 2 μV). This is so tiny that it is like the voltage in your radio antenna. Any exposed wires act like antennas and pick up signals from lights and machinery; NOT the signals in which we are interested.

  • Thermocouple extension wire used when making cables (as for attaching to a moving slide) must also be shielded.

  • Use the black Lynx cables and metal JLX junctions that carry the shield all the way back to the eDART.