> For the complete documentation index, see [llms.txt](https://docs.efento.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.efento.io/nb-iot-loggers/installation/logger-specific-installation-guidelines/4-20-ma-loggers.md).

# 4-20 mA loggers

Efento 4–20 mA loggers are engineered to measure the standard analog output of industrial sensor probes and seamlessly transmit this data over NB-IoT networks directly to Efento Cloud or your custom backend server.

## Channel compatibility and specifications

Each logger can support up to three independent analog channels, making it fully compatible with:

* 2-wire probes
* 3-wire PNP / NPN probes
* 4-wire probes

The logger is capable of measuring currents across a broad range of **-24 to 24 mA**, with a high measurement resolution of **0.001 mA**. The internal shunt resistance (Rs) for each channel is **3 Ω**.

## Connecting the probes

To wire your 4–20 mA sensors to the terminal blocks, you must first access the Printed Circuit Board (PCB) by opening the logger's enclosure.

{% hint style="warning" %}
**WARNING**: The logger must be completely powered off before connecting the probes or modifying DIP switch configurations on the PCB. Adjusting hardware switches / connecting the probes while the device is live can cause electrical shorts, lead to inaccurate sensor readings, or permanently damage the logger's internal circuitry. **To switch off the logger, press and hold the power button located on the PCB for 7 seconds until both LEDs begin to blink in a distinct shutdown sequence.**
{% endhint %}

{% stepper %}
{% step %}

#### Open the enclosure

Refer to the [Inserting the SIM card and powering](/nb-iot-loggers/installation/inserting-the-sim-card-and-powering-on.md) on section for full details on opening your specific casing model:

* IP30 Enclosures: Use a flat tool or small screwdriver to gently pry open the back panel. remove the front cover, unscrew the internal protective plastic shield (2 screws), and lift out the mainboard.
* IP67 Enclosures: Unscrew and remove the external screws securing the front and back panels together, remove the front cover, unscrew the internal protective plastic shield (2 screws), and lift out the mainboard.
  {% endstep %}

{% step %}

#### Route the cables

Route the sensor cables through the designated holes on the bottom or side of the enclosure. Feed the sensor wires through the glands before connecting them to the board.
{% endstep %}

{% step %}

#### Wire to the terminal blocks

Connect the individual wire leads of your probe to the appropriate screw terminal channels on the PCB ([Sensor probe wiring and configurations](#probes-connections-settings)). Double-check your sensor's data sheet for correct pinouts to prevent polarity reversal.
{% endstep %}

{% step %}

#### Secure the hardware settings

Before closing the device, verify that your Sensor Power DIP switch ([Power configuration](#sensor-probes-power-configurations)) and your Channel DIP switches are correctly positioned to match your specific probe type ([Sensor probe wiring and configurations](#probes-connections-settings)).
{% endstep %}

{% step %}

#### Reassemble the device

Connect the power board connector and firmly seat the mainboard back into its designated position. Place the internal plastic cover over the board and secure it with the two internal screws. Finally, close the outer casing by snapping the back panel shut (IP30) or evenly tightening the external cover screws to maintain the weather-tight seal (IP67).
{% endstep %}
{% endstepper %}

## Power configuration

The logger offers two distinct operational modes for supplying electrical power to your connected sensors: **logger-powered (passive mode)** and **externally powered (active mode)**.

<details>

<summary><strong>Logger-powered probes (passive mode)</strong></summary>

### Logger-powered probes (passive mode)

Efento 4–20 mA loggers feature an internal, regulated voltage source capable of supplying up to **18 V and 30 mA** to power connected passive probes (supporting 2-wire, 3-wire PNP/NPN, and 4-wire configurations). This internal power line is fully equipped with built-in over-current and short-circuit protection to safeguard both the logger and your sensors.

* Configuration: This hardware setting is manually configured via the onboard DIP switch labeled "Sensor Power".
* To Enable: Toggle the "Sensor Power" DIP switch to the ON position.

<figure><img src="/files/jd0UlRZ62s3YUrTeuwo6" alt="" width="563"><figcaption></figcaption></figure>

</details>

<details>

<summary><strong>Externally powered probes (active mode)</strong></summary>

### Externally powered probes (active mode)

Alternatively, you can choose to power 2-wire, 3-wire PNP, and 4-wire probes using an independent external power supply.

{% hint style="warning" %}
**CRITICAL COMPATIBILITY NOTE**: 3-wire NPN probes cannot be powered by an external source; they must always rely on the logger's internal power supply.
{% endhint %}

* Configuration: When routing power through an external loop, the logger's internal power delivery must be isolated to prevent electrical conflicts.
* To Disable: Toggle the "Sensor Power" DIP switch to the OFF position.

<figure><img src="/files/Xr1ft4vnsRYZ9RcJv9ki" alt="" width="563"><figcaption></figcaption></figure>

</details>

## Sensor probe wiring and configurations

By default, Efento 4–20 mA loggers are equipped with **2 measurement channels**. A **3rd channel is optional** and must be specified at the time of ordering.

Each channel must be manually configured to match your specific probe type (2-wire, 3-wire, or 4-wire) using the dedicated hardware switches located directly on the PCB:

* Channel 1 configuration: adjusted using DIP switches J1 and J2.
* Channel 2 configuration: adjusted using DIP switches J3 and J4.
* Channel 3 configuration (optional): adjusted using DIP switches J5 and J6.

Wiring schemes depend on the selected power source type. For the wiring diagram of the used probe and external power supply contact the corresponding manufacturers.

### Logger-powered probes (passive mode)

<details>

<summary><strong>2-wire passive mode (probes powered by Efento logger)</strong></summary>

#### **2-wire passive mode (probes powered by Efento logger)**

The required configuration of the DIP switches is summarized in the table below.&#x20;

| Channel number | Switch state               |
| -------------- | -------------------------- |
| 1              | <p>J1 = ON<br>J2 = OFF</p> |
| 2              | <p>J3 = ON<br>J4 = OFF</p> |
| 3              | <p>J5 = ON<br>J6 = OFF</p> |

PCB location and settings of all the switches is shown in the figure below.

<figure><img src="/files/X5zcVZCSp5q3AELwMGDJ" alt="" width="563"><figcaption></figcaption></figure>

Wiring diagram:

<figure><img src="/files/6TNomvE0uMypXdrpqf00" alt="" width="563"><figcaption></figcaption></figure>

</details>

<details>

<summary><strong>3-wire PNP passive mode (probes powered by Efento logger)</strong></summary>

#### &#x33;**-wire PNP passive mode (probes powered by Efento logger)**

The required configuration of the DIP switches is summarized in the table below.&#x20;

| Channel number | Switch state               |
| -------------- | -------------------------- |
| 1              | <p>J1 = ON<br>J2 = OFF</p> |
| 2              | <p>J3 = ON<br>J4 = OFF</p> |
| 3              | <p>J5 = ON<br>J6 = OFF</p> |

PCB location and settings of all the switches is shown in the figure below.

<figure><img src="/files/Q0aQSHmXC6rWYfJl0ifS" alt="" width="563"><figcaption></figcaption></figure>

Wiring diagram:

<figure><img src="/files/tPYduiVN6ZkgaHTfxzKF" alt="" width="563"><figcaption></figcaption></figure>

</details>

<details>

<summary><strong>3-wire NPN passive mode (probes powered by Efento logger)</strong></summary>

#### **3-wire NPN passive mode (probes powered by Efento logger)**

The required configuration of the DIP switches is summarized in the table below.&#x20;

| Channel number | Switch state               |
| -------------- | -------------------------- |
| 1              | <p>J1 = OFF<br>J2 = ON</p> |
| 2              | <p>J3 = OFF<br>J4 = ON</p> |
| 3              | <p>J5 = OFF<br>J6 = ON</p> |

PCB location and settings of all the switches is shown in the figure below.

<figure><img src="/files/ZyvEA3AKwHf0Jiu2TvQS" alt="" width="563"><figcaption></figcaption></figure>

Wiring diagram:

<figure><img src="/files/zLn2mhgmg3LA25xMPBre" alt="" width="563"><figcaption></figcaption></figure>

</details>

<details>

<summary><strong>4-wire passive mode (probes powered by Efento logger)</strong></summary>

#### **4-wire passive mode (probes powered by Efento logger)**

The required configuration of the DIP switches is summarized in the table below.&#x20;

| Channel number | Switch state                |
| -------------- | --------------------------- |
| 1              | <p>J1 = OFF<br>J2 = OFF</p> |
| 2              | <p>J3 = OFF<br>J4 = OFF</p> |
| 3              | <p>J5 = OFF<br>J6 = OFF</p> |

PCB location and settings of all the switches is shown in the figure below.

<figure><img src="/files/PQTrSUA4jtB8jYsFOTpx" alt="" width="563"><figcaption></figcaption></figure>

Wiring diagram:

<figure><img src="/files/hz0ygqCbNjRwYUBWAnbb" alt="" width="563"><figcaption></figcaption></figure>

</details>

### Externally powered probes (active mode)

<details>

<summary><strong>2-wire active mode (externally powered)</strong></summary>

#### **2-wire active mode (externally powered)**

The required configuration of the DIP switches is summarized in the table below.&#x20;

| Channel number | Switch state               |
| -------------- | -------------------------- |
| 1              | <p>J1 = ON<br>J2 = OFF</p> |
| 2              | <p>J3 = ON<br>J4 = OFF</p> |
| 3              | <p>J5 = ON<br>J6 = OFF</p> |

PCB location and settings of all the switches is shown in the figure below.

<figure><img src="/files/X5zcVZCSp5q3AELwMGDJ" alt="" width="563"><figcaption></figcaption></figure>

Wiring diagram:

<figure><img src="/files/GtFmrGFnailvDY0TSYE3" alt=""><figcaption></figcaption></figure>

</details>

<details>

<summary><strong>3-wire PNP active mode (externally powered)</strong></summary>

### **3-Wire PNP active mode (externally powered)**

The required configuration of the DIP switches is summarized in the table below.&#x20;

| Channel number | Switch state               |
| -------------- | -------------------------- |
| 1              | <p>J1 = ON<br>J2 = OFF</p> |
| 2              | <p>J3 = ON<br>J4 = OFF</p> |
| 3              | <p>J5 = ON<br>J6 = OFF</p> |

PCB location and settings of all the switches is shown in the figure below.

<figure><img src="/files/Q0aQSHmXC6rWYfJl0ifS" alt="" width="563"><figcaption></figcaption></figure>

Wiring diagram:

<figure><img src="/files/CGuCBnRGWSHeDsbBlDaj" alt=""><figcaption></figcaption></figure>

</details>

<details>

<summary><strong>4-wire active mode (externally powered)</strong></summary>

#### **4-wire active mode (externally powered)**

The required configuration of the DIP switches is summarized in the table below.&#x20;

| Channel number | Switch state                |
| -------------- | --------------------------- |
| 1              | <p>J1 = OFF<br>J2 = OFF</p> |
| 2              | <p>J3 = OFF<br>J4 = OFF</p> |
| 3              | <p>J5 = OFF<br>J6 = OFF</p> |

PCB location and settings of all the switches is shown in the figure below.

<figure><img src="/files/PQTrSUA4jtB8jYsFOTpx" alt="" width="563"><figcaption></figcaption></figure>

Wiring diagram:

<figure><img src="/files/sV4Iv6O5jaGwffji96GW" alt=""><figcaption></figcaption></figure>

</details>


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