The LR Series input circuits feature intelligent signal conditioners using a separate ASIC microprocessor as the controller for each channel.
High accuracy measurement: To reduce the high-sensitivity amp offset in the voltage divider and amplifier sections, which handle levels from 100 au F.S. to 200 V F.S., the internal zero error is A/D converted, and an offset voltage is provided by the D/A converter in the auto canceler. The gain error of the potential divider and amplifier are measured with high accuracy during production and written to a non-volatile semiconductor memory for use in calibration compensation. Auto calibration is performed before each measurement by applying zero and full-scale inputs to the A/D converter.

• Noise immunity

  Noise immunity is a major performance criterion for lab-use recorders, which must operate in severe environments. Thus, the microprocessor performs digital filtering in addition to analog filtering, for even greater rejection of normal mode noise.
  The common mode noise influence is drastically reduced by totally isolating each circuit from all others with photocouplers and individual floating power supplies.

• High reliability

  Semiconductor technology is used extensively throughout the circuits for the highest reliability. For example, scale and zero adjustment pots, a frequent cause of failure, have been replaced by calibration data written into nonvolatile memory. In addition, the input circuitry is protected at all times by circuitry that senses overvoltages due to incorrect connections and switches the voltage divider to prevent damage.

• Sophisticated measurement

  All thermocouple and RTD inputs are digitally linearized, and thermocouple zero point compensation is performed digitally using a transistor temperature sensor in the terminal board. The universal input circuits digitize at a 135 Hz rate.

With the increasing use of digital technology in the electronic circuits of measuring instruments, good noise immunity is essential. Noise itself is difficult to represent quantitatively, and noise in the field is often sporadic. If noise gets through to the microprocessor section, program execution may be disturbed, resulting in "run away"; in a recorder, this may cause a pen to lock up at one side of the chart, or cause an erroneous digital value to be displayed, or disrupt chart feed.
Yokogawa has designed evaluation tests with fixed test conditions through which noise immunity can be verified. Although various noise tests are conducted, a test using high-frequency pulse noise to which digital systems are especially susceptible is described below. This test attempts to cause operating errors by applying a 1 ns rise-time pulse (time for pulse to rise from 10 to 90% of its peak value), which can cause malfunctions as it enters the circuits through stray capacitances. The noise bandwidth in this test reaches several GHz, making this the most difficult form of noise to protect against. In the Figure 6, an LR8100E is being tested for noise immunity by applying high-frequency pulse noise to its input terminals in common mode. In this example, there was no disturbance to the digital subsystems even with the maximum output of 1 kV peak. Similar tests have been performed for noise introduced in the power supply lines as well, using different test equipment, and no program execution errors have occurred even at peak values up to 2 kV.