How Far Can I Extend Water Meter Encoder Cables?… and How Can I Reduce Adverse EMI Effects Upon Flow Meter Signals?

A question that I frequently receive is, “How far away may I install an EtherMeter/ TheMeterDisplay/ Signalizer from an encoder-type flow meter?”

I also am occasionally asked, “How may I reduce the effect of EMI (ElectroMagnetic Interference) upon a flow metering instrumentation system?”

The purpose of this article is to provide practical advice that will lead to maximizing the allowable distance from instrument to flow meter, and to provide additional techniques which will lead to SCADA/meter signaling that is unaffected by nearby EMI noise sources.

Maximum Allowable Distance, And How to Achieve It…

Personal and customer-reported experience has shown that cable distances up to 50 feet in the absence of EMI noise sources are generally easily achieved; and — with good wiring practices — even distances up to 500 feet are possible.

The challenge stems from the encoded transmission signal type. Neptune and Sensus protocols are based upon a voltage level-based communication method that performs well when differences in ground potential are minimal. This is generally the case when the water meter and the reading equipment are installed together in close proximity. However, at longer cable distances, common-mode interference can creep in and lead to communication breakdown.

The likelihood of meter signal degradation increases when the equipment is installed in the presence of EMI (Electro-Magnetic Interference) generating equipment, such as Variable Frequency Drives, Electric Motors, and Welders.

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Recommendations

1. In order to achieve optimal performance of a meter-reading device over extended wire distances, we recommend the use of shielded instrumentation cable, such as Belden 8771 or Carol (General) Cable C2526A. Both are jacketed cables with three (3) 22AWG conductors, a shield, and a drain wire.
2. The Belden 8771 and Carol C2526A cables feature three (3) color-coded conductors: RED, WHITE, BLACK; and the water meter cables usually feature conductors color-coded: RED, GREEN, BLACK. For simplicity, splice as follows: RED-RED, BLACK-BLACK, WHITE-GREEN.
3. Special Case: Zenner Stealth Ultrasonic Flow Meter, Encoder Cable (Mains-Powered Version). Recommended Extension Cable: Alpha Wire 1295C SL002 Multiconductor Cable, 5C, 22 AWG, Foil Shield, Gray PVC, 500, 1295 Series (Colors = Red, Green, Black, Orange, White). Available HERE.
4. Bond the drain wire to ground at one end of the cable only (generally at the meter-reader end).
5. Minimize overall cable distance by cutting off unnecessary, extra cable.
6. Bond the water meter body to control panel ground with a dedicated 14AWG wire.
7. Power the meter reading device (EM.100 EtherMeter or EMP Signalizer) with a dedicated DC Power Adapter (no other devices powered by the adapter).
8. For mains-powered water meter reading devices (EM.100 EtherMeter and EMP Signalizer), use an isolated AC-DC power adapter, such as the SCADAmetrics MDR.20.24. For especially-challenging wire distance applications, a higher-capacity HDR.100.24 is recommended (not because of its higher-amperage (4A/100W) capacity, but because of its increased class 2 isolation and increased noise-filtering capability).
9. Minimize the distance between the DC Power Adapter and the Meter Reading Instrument.
10. For stations that feature VFDs (Variable Frequency Drives), installation of Line Reactors will reduce the amount of harmonic noise fed back into the station’s AC power bus.

Of the above recommendations, #1-4 are considered necessities, whereas #5-8 may be reserved for tackling particularly problematic situations.

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But I Need to Interface an EtherMeter-based SCADA System with a Water Meter 1000 Feet Away?…

Sometimes, due to extreme distance or the presence of strong EMI, another signal-extension approach is needed. In the case of extending the signal from a flow meter to a SCADA system, in the context of a model EM.100 EtherMeter… The EtherMeter should be installed in close proximity to the flow meter, and then the RS.485 port of the EtherMeter can be leveraged to achieve long-distance backhaul communications.

A 4-Conductor, low-voltage, shielded extension cable can be used to extend both the power (24vdc) and Modbus/RTU (RS.485) signals across a long distance. Carol/General Cable C1352A or Belden 8723 (22AWG, shielded) are recommended:

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But I Need to Interface a Signalizer-based SCADA System with a Water Meter 1000 Feet Away?…

In the case of extending the signal from a flow meter to a SCADA system, in the context of a model EMP Signalizer… The EMP Signalizer should be installed in close proximity to the flow meter, and then its pulse and milliamp ports can be leveraged to achieve long-distance backhaul communications. (4-20mA and Pulse signaling is much more forgiving of long distances than encoder signals).

An 8-Conductor, low-voltage, shielded extension cable can be leveraged to extend the following power & signal pairs across a long distance:

• 24Vdc Power (low voltage pair)
• 4-20mA (low voltage pair)
• Pulse per Volume (dry contact pair)
• Meter Fault (dry contact pair)

Belden 9305 (22AWG, shielded) is recommended:

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EMI Reduction — Illustrated Techniques

The following illustration demonstrates the various technologies and techniques that may be applied to reduce/eliminate EMI-induced meter communication problems.

When these wiring principles are put into practice, we have observed customers achieve successful meter communications up to 500+ cable feet. Of course, each application is unique, and thus your experience may differ.

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Enhanced Power Supply Isolation Techniques

Another method available to drastically reduce the level of EMI noise effects upon a Signalizer and Flow Meter circuit is to install a medical-grade isolation transformer. Medical-grade transformers are ideal for protecting sensitive electronic equipment in hospital (and industrial) environments. Faraday shielding reduces the cumulative leakage current of the Isolator and connected equipment to levels less than 100 microamps. These transformers remove EMI/RFI noise, utility switching transients, and harmonics generated by other on-site loads. Additionally, medical-grade transformers reduce the impact of utility-related surge conditions. Their inherent filtering provides continuous common-mode noise rejection with no wearable moving parts. Example models include the Model MD-250-U (Triad Magnetics) and the Model IS-500 (Eaton/Tripp-Lite).

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Enhanced Meter Grounding Techniques

Another method available to reduce the level of EMI noise effects upon a Signalizer and Flow Meter circuit is to ground the signal common wire.

For metering systems that contain a AMI endpoint, only the signal common is grounded: Signalizer Terminal #6 (AMI.CMN).

For metering systems that DO NOT contain an AMI endpoint, all signal wires may be connected to ground: Signalizer Terminals #4 (AMI.CLK), #5 (AMI.DATA), and #6 (AMI.CMN). Note that Signalizer momentarily disconnects terminals #5 and #6 from the meter during the meter reading operation.

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Questions?…

Are you interested in learning more about how SCADAmetrics flow instrumentation, when implemented with good wiring practices, can provide reliable and accurate signaling to your SCADA, Telemetry, or Building Automation System? Give us a call!… We’ll be glad to discuss the details!