A: The data logger can provide sensor power. On the ML-x17’s, the excitation voltage is fixed to 12V. (It can be changed to 24V by soldering jumper SJ1).
Extra (sensor) output (5V, 12V or 24V through jumper selection) is available when a ML-OP-524 option board is mounted in the data logger.
The data logger is designed for low-power applications. Both data logger and ML- OP-524 option board have a power circuit delivering maximum 2.4 Watt.
(Specs: 200mA @12V, 2.4 Watt).
| ML-x17(Soldering jumper selection) | ML-OP-524 (Jumper selection) |
| 200mA @5V | |
| 200mA @12V | 200mA @12V |
| 100mA @24V (SJ1 soldering jumper) | 100mA @24V |
However… The chip used in the ML-x17 power circuit is end of life and no longer available.
On the ML-525 series, the sensor excitation voltage is selectable through the menu between 3 and 21V.
The maximum power has the same value’s as on the ML-x17: 2.4Watt.
(Specs: 200mA @12V, 2.4Watt).
| ML-525xx (Menu, voltage selection) |
| 200mA @ >3 .. 12V |
| 100mA @ >12 .. 21V |
Be aware that the 100 or 200mA is an absolute maximum. (Depending on the selected voltage).
Sensors drawing more current, will trigger the over current protection in the power circuit and shut down the sensor power.
Especially, sensors with high capacitance value (causing a short, high power-on current) will not match the data logger specs.
From firmware version V5.1 B2, the sensor power has soft-start ramping implemented to limit inrush current caused by sensor input capacitance.
The power-build-up method had to be changed because of the sensor power circuit (chip) change. On the ML-x17 a few “spikes” are generated during sensor power-on. On the ML-525 power circuit chip, spike generating isn’t possible. During the sensor power on, the current is temporarily limited and therefore, the voltage will slowly raise from zero to the configured value. The sensor power voltage will be available as long as the current drawn from X4 is lower than the 200 mA limit.
T: Advice when the data logger and sensor configuration is migrating from ML-x17 to an ML-525xx, mount and test sensors in the workshop, on a ML-525xx, if power remains.
T: If the power is cut off during sensor power up, check the initial sensor start-up current. It should be mentioned in the data sheet of your sensor.
T: When experiencing problems, mount a resistor, in series with the positive sensor power wire on the X4 connector.
Start with a value of 120 ohm, this will limit the current to 100mA. If that works, try to lower the value to a value 100 .. 12 ohm.
Be aware: The serial resistor will lower the actual sensor voltage. It can be calculated:
Lowered sensor voltage = Sensor power voltage – (Sensor continue current x Resistor value)
Example:
Selected sensor voltage = 12V (Data logger menu)
Sensor continue current = 10mA (Sensor data sheet)
Sensor min./max. voltage = 12V +/- 10% (Sensor data sheet)
Resistor = 120Ohm
These values will result in:
Sensor power-up current limitation = 100mA (12V/120Ohm).
The actual sensor voltage when a 120Ohm resistor is mounted in series = 10,8V (12 V – (0,01A x 120Ohm)
Check if your sensor will work at 10,8 Volts. (Yes it will, 12V – 10% = 10,8V)
.
