Scaling JUMO 401001 Pressure Sensor with Siemens LOGO! AM2

Scaling JUMO 401001 Pressure Sensor with Siemens LOGO! AM2

This reference covers the integration of a JUMO 401001 relative pressure transmitter (0–16 bar, 4–20 mA, 10–30 V DC, 3-wire) into a Siemens LOGO! 8 base module via an LOGO! AM2 analog input expansion. It documents the required wiring, the mA-to-bar transfer equation, the LOGO! Soft Comfort configuration for engineering-unit scaling, and the field verification steps that confirm end-to-end accuracy.

1. Sensor Specifications

The JUMO 401001 family is a relative-pressure transmitter for gaseous and liquid media. The values below correspond to the 3-wire, current-output variant referenced in this article; consult the JUMO pressure transmitter catalog and the device-specific data sheet for the exact shipped configuration.

Output current for any pressure P (bar) inside the calibrated range:

I_out (mA) = 4 + (P / 16) × 16 = 4 + P

This produces the linear lookup shown below.

2. LOGO! AM2 Module Hardware

The LOGO! AM2 (Siemens part number 6ED1055-1MA00-0BA2 for the LOGO! 8 generation, -0BA1 / -0BA0 for earlier versions) is a 2-channel analog input expansion. Both channels are individually configurable for either voltage or current. The AM2 RTD variant (6ED1055-1MD00-0BA2) is a different module and is not covered here.

The raw value delivered to the LOGO! CPU is always normalized to 0–1000 across the configured sensor span. With the AM2 set to 4–20 mA, a live-break (< 4 mA) condition reads 0, and 20 mA reads 1000. This 10-bit raw value is what the CPU program scales into engineering units.

For configuration of the AI channels in the LOGO! base see the Siemens LOGO! system manual.

3. 3-Wire Wiring

The JUMO 401001 3-wire variant uses a dedicated supply pair and a separate signal conductor that sources current proportional to pressure. The AM2 channel reads the current on its input while sharing the same 24 V ground reference.

1. Connect V+ (red) of the JUMO 401001 to the 24 V supply rail.
2. Connect V− (black) of the JUMO 401001 to the 0 V rail (same reference as the AM2 M terminal).
3. Connect the Sig (brown) wire of the JUMO 401001 to the AM2 AI1 input terminal.
4. Bridge the AM2 M terminal to the 0 V rail.
5. In LOGO! Soft Comfort, configure AI1 sensor type as 4..20 mA (not 0..20 mA) — see Section 5.

4. Scaling Mathematics

The transfer function from the LOGO! raw value (0–1000, where 0 = 4 mA and 1000 = 20 mA) to bar is:

P (bar) = (Raw / 1000) × 16 = Raw × 0.016

Equivalently, in integer math suitable for LOGO! fixed-point scaling blocks:

P (bar × 100) = Raw × 16 / 10

This produces 0–1600 (i.e. 0.00–16.00 bar with two decimal places) and avoids floating-point rounding on a LOGO! that does not support native float for that arithmetic path.

Gain and offset form

The LOGO! Analog Amplifier block (and the AI scaling fields on the LOGO! 8 base) accept a gain g and offset b:

Out = (In × g) + b

With In = raw (0–1000), Out = pressure in bar:

5. LOGO! Soft Comfort Configuration

The procedure below uses LOGO! Soft Comfort v8.3 / v8.4 (compatible with LOGO! 8 6ED1052-xxyy8-0BA2 base modules). Earlier 0BA0 / 0BA1 hardware uses the same data fields but may require the legacy Analog Amplifier block.

5.1 Configure the analog input

1. In the programming tree, open Inputs → AI1 and select Analog Input.
2. Set Sensor type to 4..20 mA.
3. Enable On and Sensor connected.
4. Under Sensor, set Min 0 / Max 16 bar (these are the engineering-unit endpoints used by the LOGO! display and web server).
5. Under Sensor range, set Min 4 mA / Max 20 mA (this is the electrical range that the AM2 reads).
6. Set the display Decimal places to 1 for 0.0–16.0 bar readout, or 2 for 0.00–16.00 bar.

5.2 Map the scaled value to a flag

1. Drag the AI1 scaled output onto the LOGO! display (a default text message block already shows the input).
2. For downstream logic (pump control, alarm thresholds, etc.), reference the AI1 value directly — it is already in bar.
3. If the program needs the raw integer (0–1000), place an Analog Amplifier block (gain = 1.0, offset = 0) on the same signal, or use the un-scaled AI reading.

5.3 Equivalent ladder / FBD snippet (LOGO! FBD view)

AI1 [sensor: 4..20 mA | range: 0..16 bar] ──▶ Display "Pressure = XX.X bar"
                              │
                              ├──▶ Threshold trigger Q1 (cut-in @ 6.0 bar)
                              └──▶ Threshold trigger Q2 (cut-out @ 4.5 bar)

6. Worked Numerical Examples

Raw value is derived from Raw = (I − 4) / 16 × 1000 = (I − 4) × 62.5. The integer rounding inherent in the 10-bit AM2 conversion limits absolute resolution to ~16 mbar per step at the 0–16 bar span — adequate for pump staging, leak detection, and trend logging, but verify against your process accuracy target.

7. Verification Procedure

Perform these four checks after wiring but before relying on the readout in control logic.

7.1 Loop-current check (sensor powered, process depressurised)

1. Break the signal wire at the AM2 AI1 terminal.
2. Insert a digital multimeter in mA mode in series with the wire.
3. Apply 0 bar to the sensor (vent to atmosphere for relative-pressure types).
4. Expected reading: 4.00 mA ± 0.05 mA.
5. Apply a known reference pressure from a dead-weight tester or hand pump.
6. Confirm: I = 4 + P(mA) where P is the bar value (e.g. 8.00 mA at 4.00 bar).

7.2 LOGO! raw value check

1. Reconnect the signal wire.
2. In LOGO! Soft Comfort online mode (or on the LOGO! base display under AI1), read the unscaled AI1 value.
3. At 0 bar it must read 0; at 16 bar it must read 1000 ± 1.
4. If it reads pegged at 1000 with low pressure, check for shorts in the signal wire or a sensor with a powered output wired against polarity.

7.3 Scaled-display check

1. Apply three reference points (e.g. 0 bar, 8 bar, 16 bar) using a calibrated source.
2. Compare the LOGO! display (or web server readout) against the calculated value.
3. Tolerance: ± 0.1 bar at the 0–16 bar span, dominated by the AM2 10-bit quantisation (~0.016 bar/step) and the sensor linearity spec.

7.4 Open-loop diagnostic

1. Disconnect the JUMO signal wire at AI1.
2. The LOGO! AI1 raw value must drop to 0 (4 mA live-zero is interpreted as 0 in 4..20 mA mode).
3. If the value holds at the previous reading, the AM2 firmware is set to a different sensor type (e.g. 0..20 mA) — re-check Section 5.1 step 2.

8. Troubleshooting Matrix

9. Edge Cases and Field-Proven Caveats

• 2-wire variant. If the shipped sensor is 2-wire instead of 3-wire, the loop is powered through the AM2 itself. The AM2 does not source loop power; an external 24 V with a 250 Ω sense resistor at the AI terminal is required, and the sensor's supply + and signal + become the same conductor.
• Voltage-mode misuse. Configuring the AI for 0..10 V while feeding 4..20 mA produces 1.0 V at 4 mA — the LOGO! reads 100 raw units and displays 1.6 bar at zero pressure. This is the most common commissioning mistake.
• Cold-junction effects. The JUMO 401001 zero and span drift with temperature. Verify the application requires either the standard (≤ 1 % / 10 K) or the compensated (≤ 0.2 % / 10 K) variant.
• EMI on shared cable trays. VFD output cables routed parallel to the signal cable inject common-mode noise. Maintain ≥ 200 mm separation or use shielded, twisted-pair cable bonded at the panel end.
• LOGO! 0BA0 vs 0BA2. The legacy 0BA0 base (firmware < 1.08) does not support AI scaling fields — scaling must be performed manually with an Analog Amplifier block. The procedure in Section 5 still applies once the gain/offset is set: g = 0.016, b = 0.
• Web server display. On LOGO! 8 with the integrated web server (firmware ≥ 1.08.x), AI1 is exposed as AI1 in the user-defined variable list. Tag it with the unit suffix "bar" in the Variable table for unambiguous HMIs.

10. Related Sensor Ranges

The same scaling procedure applies to other JUMO 401001 ranges; only the gain and display maximum change.

For the bi-polar range (−1 to +9 bar), set g = 0.010 and b = −1.0 in the AI scaling fields.