• Input: What signal will control the resistance simulation output? Will it be an analog current signal of 0/4...20mA, a voltage signal of 0...10V, or perhaps it's simply to ensure galvanic isolation between the Pt100 sensor and the controller's RTD input? The simulator output can also be controlled via RS485 Modbus serial transmission. The RS485 port is available as an alternative way to control the resistance simulator output, regardless of the simulator's analog input.

• Output: In what range (Rmin...Rmax) should resistance simulation be possible? Rmin and Rmax should be specified, remembering that Rmin must be greater than 30Ω (this is caused by the resistance of series elements within the simulator, such as the controller's RTD input current measuring resistor, fuse, etc.). The output circuit hardware is selected based on the Rmin...Rmax values specified in the order. The declared device class of 0.1% is defined relative to Rmax. This means that subsequent use of only a much narrower subrange than the range defined in the order will be subject to a greater error than would be possible with a correctly defined range in the order.
  Example: when defining the output as 0....10kΩ, the declared accuracy of the simulated resistance will be 0.1%⋅10kΩ=10Ω. Furthermore, the realization of zero will in fact be a value of ~30Ω. Using only the range, e.g. 100...200Ω, will result in an accuracy of ±10Ω, which is 10% of the used range (although in reality it is much better) instead of the achievable class of 0.1%.

• Measuring current: What current does the controller use to measure the connected, in this case simulated, resistance? The simulator's output hardware must be set to be able to measure the current, which is used to set the voltage at the terminals—thus simulating resistance according to Ohm's Law. A simulator ordered with a measuring current of, for example, max 1mA will not be able to operate correctly with an actual current of 2mA, because it will be outside its dynamic measurement range. On the other hand, ordering a simulator with a max current with a large margin (e.g., 5mA, when the actual flow is 0.1mA) will result in a loss of accuracy, similar to specifying too high Rmax value.
  In this case, the Simulator-R will continue to work correctly, because the current given in the ordering code is the maximum measured current (the smaller one will still be measured, so the resistance will be simulated).
  In the case of a simulator of type SIM-R-MUX, because it is designed to work with pulsed measuring current, the device will only operate correctly within the range of ±30% of the current specified in the ordering code - therefore it is necessary to provide the real value of the current output by the controller.

• Nonlinearity: This parameter is optional. It does not apply when ordering a resistance simulator solely to act as a separator (e.g. with a Pt100 input and Pt100 output so 1:1 operation). When controlling the output via RS485 Modbus transmission, it is also irrelevant, because the resistance value you want to achieve at the output is entered in the appropriate register - there is no conversion of two different signal standards. This parameter may be important when ordering a device in a version that simulates the Pt100 value which is controlled by an analog signal, e.g. 4...20mA. By default, the simulator simulates the output resistance linearly with respect to the control signal. The control signal is an indirect signal with values 0...10000 (0...100.00%). The input signal is normalized to this range (e.g. 4mA ⭢ 0, 12mA ⭢ 5000, 20mA ⭢ 10000). The Pt100 sensor does not have a linear characteristics of the resistance with temperature, it is curved. The resistance simulator has a 10-point table available, using which you can enter the desired curvature (the 10-point approximation table is not available in the SIM-R-MUX version).
  Below is an example for a 0…10V input and a Ni1000 sensor -60…+200°C (which, according to the table, corresponds to a resistance of 695…2407Ω):

  a) The output simulates the resistance linearly to the input signal (standard version of Simulator-R).

  Input [V]	Resistance [Ω]	Temperature [°C]
  0	695	-60
  5	(2407+695)/2=1551	około 90
  10	2407	200

  b) The output has a 10-point table implemented, obtaining a characteristic curve similar to the actual characteristic of the Ni1000 sensor.

  Input [V]	Temperature [°C]	Resistance [Ω]
  0	-60	695
  5	(200+60)/2=70	1417
  10	200	2407

  As you can see in this example, the difference in performance is significant - as much as 20°C. For a different sensor and range, this difference may be negligible. However, this should be kept in mind when ordering, knowing what's needed for a given application. Often, the resistance value can be converted to temperature in the PLC itself.

2. Measurements

Typically, the RTD input circuit is a current source (with a constant current value) or a voltage source E with a series resistor Rs (then the current value changes depending on the connected resistance).

If the datasheet does not provide information about the resistance sampling current, you can measure it with a simple multimeter.

If the voltmeter/ammeter readings are close to zero when making the following measurements, it probably means that the RTD input is giving a pulsed measurement current (which the multimeter cannot measure and averages to zero). In this situation, all that remains is to make the following voltage measurements using a probe with an oscilloscope.