Connecting 10 kg Load Cell to LOGO! 8: WISE-4010 vs ADAM-6017

1. Problem Definition: 1 g Resolution on a 10 kg Load Cell with LOGO! 8

Reading a 10 kg load cell to a 1 g displayed resolution (10 000 engineering units across 0–10 000 g) is a common but deceptively demanding requirement for the Siemens LOGO! 8 logic module family. The base LOGO! BM (basic module) provides on-board analog inputs with a 10-bit internal representation (0–1 000 raw counts) and accepts only voltage (0–10 V) at its AM2 / AM2 PT100 expansion terminals. That native resolution is roughly one order of magnitude coarser than the 1 g target and is therefore unsuitable for weighing applications without an external high-resolution remote I/O module and a load cell signal conditioner.

Two Advantech remote I/O modules are commonly paired with LOGO! 8 in this role:

• WISE-4010/LAN – 4 universal analog inputs, 12-bit resolution, RESTful web API, Modbus/TCP server.
• ADAM-6017 – 8 analog inputs, 16-bit resolution, Modbus/TCP server, isolated 2 500 V_DC.

Both can publish scaled and unscaled process data over Modbus/TCP, which the LOGO! 8 can poll using the client block network. The defining engineering question is which module supports 1 g resolution across a 10 kg span, and which auxiliary hardware (load cell amplifier) is required to condition the millivolt bridge output into a signal the analog input can digitise cleanly.

2. Why a Dedicated Load Cell Amplifier Is Mandatory

A strain-gauge load cell is a passive Wheatstone bridge. With 10 V excitation the full-scale output of a typical 2 mV/V cell at 10 kg is:

V_out = V_exc × sensitivity = 10 V × 0.002 = 0.020 V = 20 mV

This signal sits 1 000× below the 0–10 V LOGO! on-board AI range and roughly 50× below the 0–20 mA current-loop range. The signal is also low-impedance, bipolar around the no-load null, and contaminated with thermal EMF, lead resistance, and common-mode noise from the 50/60 Hz mains environment.

A load cell amplifier performs four functions that the LOGO! 8 or any general-purpose AI cannot perform alone:

1. Stable, low-noise bridge excitation (typically 5 V or 10 V regulated).
2. Instrumentation-grade differential amplification with high CMRR (> 100 dB typical).
3. Offset/tare trimming and span calibration.
4. Conversion to a robust industrial signal – most commonly 0/4–20 mA or 0–10 V – that can be run over shielded twisted pair back to the analog input.

3. Recommended Component Stack

4. Resolution Analysis: 12-bit WISE-4010 vs 16-bit ADAM-6017

With the KFD2-WAC2-1.D configured for a 0/4–20 mA output mapped to 0–10 000 g, the analog input determines the smallest step the LOGO! can ever see.

The 10 000 g / 4 096 counts calculation of the WISE-4010/LAN yields 2.44 g per LSB, which mathematically prevents a 1 g display step. The WISE-4010/LAN is also limited to 12-bit (0–4 095) integer representation. The ADAM-6017 at 16 bits gives 65 535 raw codes across the 4–20 mA span, so 0.153 g per LSB – an order of magnitude inside the 1 g target, leaving headroom for noise, tare drift, and temperature effects.

When counting effective bits, also include the amplifier. The KFD2-WAC2-1.D is specified for ≤ 0.1 % accuracy and 12-bit internal resolution. Although its analog output is only 12-bit, the up-stream ADAM-6017 oversamples and provides the full 16-bit input range, and the noise performance of the system is dominated by the analog front end, not the digitiser. For laboratory-grade work, consider amplifiers with 16-bit native resolution such as the KFD2-WAC2-1.D paired with a 24-bit sigma-delta ADC front end (e.g. Mettler-Toledo IND780 or PT600 indicator) – but this exceeds the LOGO! 8 data path and is outside this reference's scope.

5. LOGO! 8 Numeric Range and Arithmetic Limits

The LOGO! 8 instruction set differentiates between two numeric types when scaling Modbus/TCP holding registers:

• Integer (15 bits + sign) – range −32 768 to +32 767. Used by analog input blocks, comparators, arithmetic blocks, threshold triggers, and most ladder/FBD operations.
• Floating-point (32-bit IEEE 754) – used only for display on the LOGO! TDE or the LOGO! Soft Comfort engineering display, and for internal conversion. Float values cannot be used as inputs to arithmetic or comparator blocks in firmware < V8.3.

The ADAM-6017 exposes analog input values as 16-bit unsigned integers (0–65 535) in input registers 0–7 (Modbus address 0x0000–0x0007) by default, with engineering-unit floating point available in registers 8–23 when enabled. The 16-bit unsigned word maps directly onto the LOGO! 8 integer range only if the value is kept at or below 32 767. If a count value of, for example, 60 000 is read, the LOGO! will interpret the high bit as a sign and report −5 536, breaking the scaling.

Two remedies exist:

1. Scale at the source – configure the KFD2-WAC2-1.D to deliver 0–10 V or 0–20 mA mapped to a reduced physical span (e.g. 0–5 000 g only), and let the LOGO! 8 add a high/low range selector. The WISE-4010/LAN is the better fit here.
2. Use the LOGO! 8 V8.2+ Analog Input Type – the Network AI block can be configured to interpret 16-bit registers as unsigned, applying a polarity offset of 32 768 so the value lands inside the −32 768…+32 767 signed range and the integer arithmetic blocks behave correctly.

For continuous 0–10 000 g, choose approach 2. Implementation is shown in Section 8.

6. Signal-Chain Wiring, Shielding, and Grounding

The complete signal path from sensor to LOGO! 8 is:

Load cell → 4-conductor shielded cable → KFD2-WAC2-1.D excitation/bridge terminals → 0/4–20 mA loop → ADAM-6017 (or WISE-4010/LAN) AI terminals → RJ-45 Ethernet → Industrial switch → LOGO! 8 Ethernet port.

1. Use a 6-wire load cell cable (sense + excitation pairs) when the cable run exceeds 6 m, to compensate for lead-resistance voltage drop in the excitation wires.
2. Connect the cable shield at the KFD2-WAC2-1.D ground terminal only. Do not bond at the load cell end; floating the load cell end prevents ground-loop current through the shield.
3. Power the KFD2-WAC2-1.D from a dedicated 24 V_DC branch. Do not share the DC bus with VFD or solenoid valve supplies.
4. Maintain at least 200 mm separation between the 4–20 mA loop and any 400 V or VFD output cables. Cross at 90° if a crossing is unavoidable.
5. Configure the KFD2-WAC2-1.D DIP switches (or PACTware) for 4–20 mA output, 0–10 000 g span. The unit's 0–20 mA or 4–20 mA selection is documented in the KFD2-WAC2-1.D datasheet – check the SIL/insulation block diagram to confirm terminal assignments for output 1 / output 2.

7. Scaling, Calibration, and Tare Procedure

The amplifier's 4–20 mA signal must be mapped to engineering units. With the load cell rated for 10 kg at 2 mV/V, calibration is a five-step procedure:

1. Zero the system with no load. Adjust the KFD2-WAC2-1.D "zero" trim until the output reads 4.000 mA at the ADAM-6017 input (raw count 0).
2. Apply a calibrated reference mass (e.g. 5 000 g or 10 000 g Class F1 weight). Allow 30 s thermal settling.
3. Adjust the span on the KFD2-WAC2-1.D until the output reads 20.000 mA at full scale (10 000 g).
4. Verify linearity at 25 %, 50 %, 75 % of full scale. Acceptable deviation: ≤ 0.05 % of full scale (≤ 5 g at 10 000 g).
5. Re-zero after the linearity check, because span adjustment may shift zero by a few counts.

8. Programming the LOGO! 8 Network Analog Input

LOGO! 8 firmware V8.2 introduced the Network Analog Input (NAI) block in FBD/UD programming. The block parameters for the ADAM-6017 are:

Once the NAI is placed, apply the LOGO! scaling formula to convert the 0–65 535 raw count into grams. The arithmetic block "Math1" is configured with:

Gain (GA) = 10 000 / 65 535 = 0.15259
Offset (OFF) = 0

Result (grams) = (NAI_value – 0) × GA = NAI_value × 0.15259

The arithmetic block returns a 16-bit signed value clamped to ±32 767. With 0–10 000 g the result always fits, so no clamping occurs. The output of "Math1" can drive a Comparator block to trigger a fill-complete or overload event, or feed the LOGO! TDE display block "Message Text" for HMI visualisation.

For tare, store the no-load NAI value at startup into a Retention marker (M-flag) and subtract it in a second Math block:

Net_g = (NAI_value – M_Tare) × 0.15259

The retention flag must be initialised only after the load cell has stabilised; gate its write with a 5 s on-delay driven by a digital input "Calibrate" button.

9. Verification and Acceptance Test

Commissioning is complete when the following checks pass:

1. Raw count check – at 0 g the NAI value reads 0 (± 5 counts). At 10 000 g the NAI value reads 65 535 (± 5 counts).
2. Calibrated span – with 5 000 g applied, the LOGO! display reads 5 000 g ± 5 g.
3. Repeatability – apply 10 000 g, remove, re-apply five times. Standard deviation of the displayed value should be ≤ 2 g (≈ 13 counts at 16-bit).
4. Drift – over 1 hour at constant zero load, the LOGO! reading must stay within ± 2 g.
5. Alarm thresholds – force a 10 500 g load. Confirm the LOGO! comparator triggers the high-alarm output and the LOGO! TDE displays the configured error message.
6. Communication loss – unplug the Ethernet patch cord. The LOGO! 8 raises communication error 0x03 on the NAI block within 5 s. Confirm the user-programmed fallback (e.g. hold last value) operates.

10. Troubleshooting Matrix

11. Application Checklist

• Use the ADAM-6017 (16-bit) when the engineering target is ≤ 0.2 g / count on a 10 kg cell. The WISE-4010/LAN (12-bit) is sufficient only when the target is ≥ 2.5 g / count.
• Never connect a bare load cell to a LOGO! on-board AI. The signal is too small and too noisy.
• Use a 4–20 mA current loop, not 0–10 V, when the cable run is > 5 m. The current loop is intrinsically immune to lead resistance and most common-mode noise.
• Keep the LOGO! 8 NAI block on a 200 ms or longer polling interval. Faster polling does not improve weighing accuracy because the upstream load cell and amplifier dominate the response time.
• Always program a software tare in the LOGO! 8 retention memory. Hardware tare via the amplifier is acceptable but harder to audit during a recipe change.
• If the application must log weight for traceability, push the LOGO! NAI value to a SCADA node via Modbus/TCP server (LOGO! 8 0BA2 with the LOGO! Web Editor / LOGO! Soft Comfort V8.3) – the LOGO! alone has no long-term storage.

12. FAQ