Analog measurements

With the MRL‑8E single ended voltage signals in the range of 0 to 2.5 V can be measured. The analog inputs AN3 and AN4 can also be configured to measure resistive sensors, e.g. Pt1000.

Option	Description	Terminals
Voltage 2.5	Single ended voltage input 0 … 2.5 V	AN1 ... AN4
NTC	Measures the temperature of a NTC thermistor	AN3
R meas > 2k	Measures a resistance > 2 kΩ	AN3
Pt1000	Measures the temperature of a Pt1000 temperature sensor	AN4
R meas > 1k2	Measures a resistance > 1.2 kΩ	AN4
R meas < 1k2	Measures a resistance > 0 Ω (preferably < 1.2 kΩ)	AN4
Voltage 0.3	Single ended voltage input 0 … 0.3 V	AN4
Voltage 2.5	Differential voltage input 0 … 2.5 V	AN4

The signals received from a sensor are wired in the MRL‑8E as illustrated in Figure 8.

Figure 8 Internal wiring of analog MRL‑8E inputs

Principals

The illustration below shows a sequence of two measurement cycles of three analog inputs (AN1, AN2 and AN3) and switched power supply.

Figure 9 Principal of analog measurements

At the start of each measurement interval the sensor power supply is switched on. After the specified Warm-up time each of the three analog inputs is measured sequentially at the sampling rate defined in ADC - conv. Rate (red lines). After each measurement has been completed, the sensor power supply is switched off.

If ADC filter is active, the input is measured 3 times and the data logger returns the statistic specified in ADC filter.

The measurement interval of all sensors is specified in Measurement Interval.