Sensortech Systems ST-3300 Series Technical Manual

ST-3300 Smart RF Sensor

Technical Manual

2221 E. Celsius Avenue, Unit B

Oxnard, California USA 93030

Tel (805) 981-3735

Fax (805) 981-3738

info@Sensortech.com www.Sensortech.com

ST-3300 Smart RF Sensor Technical Manual

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ST-3300 Smart RF Sensor Technical Manual

Preface

About The Manual

This manual is intended to provide a technical reference for configuring and operating the newest Sensortech ST-3300 Series Smart RF Sensors and software. Installation guidelines are provided in the Wiring and Installation document provided with the Sensor. New and experienced users will benefit from the detailed technical information and operating instructions for Sensortech hardware and software options and accessories.

In this manual, the ST-3300 Series Smart RF Sensors are also referred to by the general term “Gauge”.

Hardware Revisions and Software Versions covered by this manual:

ST-3300 Series Hardware Revision: A (and above)

ST-3300 Series Firmware Version: 0.04 (and above)

ST-3300 Series Configuration Software Version: 1.000 (and above)

The manual is organized as follows:

1. Quick Start Guide

2. Sensor and hardware installation information.

3. Sensortech software installation and PC requirements.

4. Overview of the Sensor and software configuration.

5. Overview of Product Calibration using the Sensor.

6. APPENDIX.

7. RS-485 ModBus Specifications

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Table of Contents

Preface ........................................................................................................................................................................3

About The Manual ..............................................................................................................................................3

Table of Contents .......................................................................................................................................................4

Introduction ................................................................................................................................................................6

Sensor Physical Installation ........................................................................................................................................6

System Overview ........................................................................................................................................................6

Sensor Electronics ......................................................................................................................................................8

Resonant Frequency Dielectric Measurement ................................................................................................ 11

Open Frame Planar Sensor Antenna Measurement ....................................................................................... 16

Sensor Antenna Design ........................................................................................................................................... 19

Theory of Operation ................................................................................................................................................ 20

Radio Frequency Dielectric Measurement ...................................................................................................... 20

Moisture Determination by Dielectric Measurement ..................................................................................... 21

ST-3300 Configuration Software ............................................................................................................................. 22

Minimum Host PC Requirements .................................................................................................................... 22

Software installation ....................................................................................................................................... 22

Connecting to the Sensor using the RS-485 Interface ............................................................................................. 23

RS-485 Serial Communication - Host PC/PLC/Controller to I/O Unit .............................................................. 23

ST-3300 Configuration Program Operation ............................................................................................................. 24

Main Screen – at Startup ................................................................................................................................. 24

Main Screen – Sensor Connected .................................................................................................................... 25

Setup Screen .................................................................................................................................................... 27

Diagnostics Screen ........................................................................................................................................... 28

Measure Configuration Screen ........................................................................................................................ 30

Product Configuration Screen ......................................................................................................................... 34

I/O Configuration Screen ................................................................................................................................. 35

Calibration Screen ........................................................................................................................................... 36

Offset Mode ..................................................................................................................................................... 37

Offset Calibration Procedure ........................................................................................................................... 38

Linear Mode ..................................................................................................................................................... 38

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Suggestions for taking product samples.......................................................................................................... 40

Maintenance Screen ................................................................................................................................................ 41

Pre-Zero Calibration ................................................................................................................................................ 42

Standardize Calibration ........................................................................................................................................... 43

Pre-Zero Calibration Procedure - using the Configuration Program ....................................................................... 44

Standardize Calibration Procedure - using the Configuration Program .................................................................. 44

Pre-Zero Calibration Procedure - using the I/O Unit Push-buttons ........................................................................ 45

Standardize Calibration Procedure - using the I/O Unit Push-buttons ................................................................... 45

Appendix .................................................................................................................................................................. 46

Sensor Electronics Unit External Connectors .................................................................................................. 46

I/O Unit External Connectors .......................................................................................................................... 47

I/O Unit Terminal Board Layout ...................................................................................................................... 48

I/O Unit Terminal Board Signals ...................................................................................................................... 49

Sensor Status and Error Messages .................................................................................................................. 50

ST-3300 Sensor RS-485 Communications Interface Specification ........................................................................... 51

ST-3300 MODBUS-RTU Serial Communications Interface............................................................................... 51

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ST-3300 Smart RF Sensor Technical Manual

Introduction

Thank you for choosing Sensortech for your moisture measurement and analysis needs. The Sensortech ST-3300 Series of Smart RF Sensors are designed for use in industrial environments and provide the most sophisticated on-line Sensors available, offering unmatched accuracy and reliability.

The Sensors are shipped with all the accessories and custom options ordered. Please compare the contents with the packing list to ensure all items are accounted for. If any items are missing or damaged, please contact Sensortech immediately for further assistance.

Sensor Physical Installation

Every Sensor installation is unique and specific installation instructions are provided for the most common and custom Sensor Application Interfaces. Please refer to the ST-3300 Wiring and Installation Guide for your specific application.

System Overview

The ST-3300 Series Sensor is a complete measurement and interface system where all signal processing and control functions are self-contained. It features multiple interface protocols including one isolated 4-20mA output, an RS-485 serial communication port, a Digital Input and a Product Temperature Input. Optional communications protocols include OI-6000 Operator Interface, Ethernet TCP/IP, DeviceNet, PROFIBUS, PROFINET and EtherNet/IP as well as digital inputs and outputs for external sample gating and control.

The ST-3300 System is composed of the following components:

Sensor Antenna - an antenna that is located in close proximity to the Product being measured and is either directly attached for low temperature applications or remotely located for high temperature applications. The Sensor Antenna is connected to the Sensor Electronics Unit through coaxial cables.

Sensor Electronics Unit - a NEMA rated metal enclosure which houses 2 PCB’s – the RF PCB and the Processor PCB. The RF PCB generates signals sent to the Sensor Antenna and provides frequency and voltage signals to the Processor PCB for moisture and temperature value calculations. It connects to the I/O Unit and the Sensor Antenna via M12 for power and signals as well as coaxial cables to measure product moisture. The Processor PCB controls the RF PCB and to read and manage data on the analog and digital interfaces.

I/O Unit - a NEMA rated metal enclosure which provides +/-15VDC power to the Sensor and allows the user to install wires onto the terminal blocks and connectors mounted on the I/O Unit PCB to provide AC power and external analog and digital interfaces.

Product Temperature Transducer - a user defined peripheral pyrometer or transducer module that connects to the Sensor Electronics Unit via a M4 x 4 pin connector for 4-20mA or voltage input via an M12 x 4 cable.

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Figure 1: Example of In-Kiln Open Frame Planar Sensor System

Figure 2: Example of Out-of-Kiln Open Frame Planar Sensor System

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ST-3300 Smart RF Sensor Technical Manual

Sensor Electronics

The heart of the ST-3300 is a sophisticated dielectric Sensor. The Sensor utilizes state of the art phase lock loop technology. High speed logic and ultra-high bandwidth operational amplifiers enhance performance. A microprocessor controls the RF measurement circuit and communicates with user defined protocol interfaces. Figure 3 shows a block diagram of the Sensor electronics.

Measurement is made by switching between one of three RF channels: CA, CH, CL and Sensortech Systems

developed and patented a specific method of dielectric determination using radio frequency. This is known as the resonant frequency technique. The purpose of the reference channels is to stabilize the Sensor over a wide range of ambient conditions. The three frequencies are measured by an onboard microprocessor and form the inputs to a proprietary algorithm used to eliminate most drift factors.

CA connects to the Sensor Antenna element which is in close proximity to the product being measured. CH

connects to the High Reference element and CL connects to the Low Reference element for precision reference

calculations.

Only one channel is switched in circuit per measurement sample, this forms a parallel tuned circuit with the inductor. The resonant frequency of this network constitutes the "lock frequency" of the phase lock loop.

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ST-3300 Smart RF Sensor Technical Manual

Opto/

A/R Sw

Isolator

Micro-processor and

Control Logic

Driver/

Freq. out

+12v

-12v

Isolator

Voltage

Controlled

Oscillator

Isolated Power Supply

Pin Diode Drivers

Automatic Gain Control

R R

Phase

Detector

+5v

-5v

Figure 3: Sensor RF PCB Block Diagram

The block diagram of Figure 3 shows the inductor L forming a parallel tuned circuit with one of three channel capacitances, C

. One capacitor is the Sensor electrode next to the product and the other two are reference

frequencies. Switching is performed by PIN diodes. The micro-processor sends control signals to measure each channel sequentially.

The resulting frequency measurements are:

FS = Sensor Antenna Frequency

= High Reference Frequency

= Low Reference Frequency

The raw moisture value for Moisture is calculated from the equation:

Moisture = STD * B coefficient * (DR – Pre-Zero) + C coefficient

where: B coefficient = slope

calibration coefficient for Product selected (SPAN)

C coefficient = offset calibration coefficient for Product selected (ZERO)

STD = Standardization Factor (calculated)

= calculated raw dielectric value

Pre-Zero = calculated raw dielectric value with empty Sensor – air only from Pre-Zero Calibration

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The Sensor measurement results are sent from the Sensor Electronics Unit to the I/O Unit via RS-485 interface. The I/O Unit provides +/-15V power supply for the Sensor Electronics Unit and terminal board connectors for connection of the analog and digital interface signals to the user’s process control systems.

The I/O Unit also provides local push button controls for performing the Zero and Standardize calibrations of the Sensor. The user opens the lid of the enclosure and presses the Zero button with nothing over the Sensor and the Status LED next to the button lights up to indicate a Zero calibration has been performed. The user then places a Standardization Plate over the Sensor and presses the Standardize button. The Status LED next to the button lights up to indicate a Standardize calibration has been performed.

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Resonant Frequency Dielectric Measurement

Numerous methods have been used to determine dielectric constant of a material. Radio frequency is often used for its ability to penetrate a material to a substantial depth and to be able to measure without contacting the material. Sensortech Systems developed and patented a specific method of dielectric determination using radio frequency. This is known as the resonant frequency technique.

Figure 5: Parallel Plate Capacitor with Dielectric Medium

Figure 4: Parallel Plate Capacitor with Air Medium

As previously stated, dielectric is a material property affecting the way it behaves in an electric field. A parallel plate capacitor is shown in figure 2(a). If the medium separating the plates is air or a vacuum, the capacitance is given by:

C = (ε

A) / d

⋅

where: ε

= permitivitty of free space = 8.854 x 10

-12

A = Area of plate d = separation distance of plates

When a dielectric medium separates the plates as in figure 2(b), capacitance becomes:

C = (ε

⋅

A) / d

⋅

where: ε

= dielectric constant

Thus, capacitance is directly proportional to the dielectric constant of the material in the electric field.

C = K

⋅

Parallel plate capacitance Sensors are rarely used for industrial applications; single-sided Sensors being preferred.

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ST-3300 Smart RF Sensor Technical Manual

Figure 6: Parallel Plate Capacitor Showing Flux Lines

Figure 7: Planar Sensor Antenna Showing Flux Lines

Figure 6 is schematic representation of a parallel plate capacitor showing uniform electric flux lines except at the edges where fringing occurs. The fringe field is generally undesirable in a capacitor, but in a single-sided capacitance Sensor, it is the only useful field.

Figure 7 is a cross-sectional view of a planar Sensor, most frequently used for gypsum board applications. A central element propagates an electric field to the grounded side plates. A small proportion of the field is directly between electrodes, but most is the fringe field used to penetrate the board. Figure 8 shows an example of an Open Frame Planar Sensor Antenna.

Figure 8: Example of an Open Frame Planar Sensor Antenna

Electrically, the Sensor Antenna, is simply a capacitor. The electrical analogy of the gypsum product is itself a capacitance with parallel resistance. The resistance or conductance represents the ionic conductance or dielectric loss in the board.

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ST-3300 Smart RF Sensor Technical Manual

Figure 9: Electrical Schematic of Product Coupling

Figure 10: Electrical Schematic of Equivalent Resonant Circuit

Figure 9 shows the electrical schematic of the product coupled to the capacitive Sensor. Air gap capacitance (

couples the product (

) to the Sensor (

) and must, therefore, be kept constant. Mounting the Sensor

between conveyor rollers, spaced perhaps 6mm below the plane of the rollers, ensures a constant coupling

capacitance, provided rollers are reasonably true. The capacitances may be combined as one (

mathematically incorrect, may simplistically be represented as

CT = Cs + C

) which, while

Figure 10 illustrates the resonant network formed by Sensor capacitance in parallel with product capacitance also in parallel with inductor (L). This network has a unique resonant frequency at which inductive reactance cancels capacitive reactance and network impedance is at a maximum. Impedance at resonance is actually

resistance (

)

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ST-3300 Smart RF Sensor Technical Manual

Figure 11: Electrical Schematic Example of a Resonant Circuit

Figure 12: Frequency, Phase and Impedance relationships of Resonant Network

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The resonant network is driven from a suitable RF signal through a pure fixed resistor (Ro) as shown in Figure 11. As frequency increases, the network is first of all inductive with a leading phase angle. At resonance all reactive components cancel and the circuit is purely resistive. At resonance, the signal amplitude across the resonant network is a function of only R

, Rp and amplitude of the driving signal. Ro and Rp behave as a simple potential

divider.

Using a precision phase lock loop to adjust signal frequency to maintain zero phase angle across resistor R

ensures the network is always at resonance.

Resonant frequency is defined as:

= 1 / [2π√(L

)]

⋅

The Sensor measures this frequency and a proprietary measurement algorithm combines Sensor frequency with two reference frequencies to produce a dielectric value that is essentially independent of ambient temperatures and component aging.

The resulting raw dielectric can be seen to be a function of Sensor capacitance (with product) and precision reference capacitors. Inductance and stray capacitance are eliminated.

Moisture is directly proportional to the raw dielectric.

Given a linear relationship, the instrument can now be calibrated from analytical data to fit a linear function of the form:

Moisture = a

D + b

⋅

Since capacitance C of Sensor capacitance. This is achieved by measuring Sensor capacitance when no product is present (D

is a composite of both the Sensor and the product, it is necessary to remove the influence

) and

subtracting this from future measurement in a similar way to performing a tare on a weigh scale. This action is termed 'Pre-zero' and should be performed periodically to compensate for antenna changes and product buildup on the antenna.

The primary moisture measurement of the Sensor uses the principle of dielectric determination. Since moisture has a much higher relative dielectric than most solids, it is possible to relate to moisture content. Radio frequency moisture determination, which is a penetrating measurement, has to take into account the mass of the product being measured in order to provide a percentage measurement. This is because the Sensor effectively counts the water molecules within the Sensor field. If more product is squeezed into that field, it will produce a higher moisture reading, even though the percentage water figure may be constant. In order to correct for this, the product mass, weight or density must be taken into consideration.

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ST-3300 Smart RF Sensor Technical Manual

Open Frame Planar Sensor Antenna Measurement

fringe field

product

dielectric

Doc ume

Doc

ume

air

dielectric

Figure 13: Open Frame Sensor - Radio Frequency Field Penetrating Through Product

The Figure 13 shows the typical radio electric field passing through a product. The dielectric effect of the product will be a function of its dielectric constant and the length of flux paths passing through the product (fringe field lines). The latter will be a function of product thickness and distance from the Sensor. If a parallel plate Sensor were used, the field lines would be uniform and a doubling in product thickness would produce a doubling in dielectric. The Sensor shown is a single sided or Planar Sensor Antenna, with a non-linear field. Doubling of product thickness will cause an increase in dielectric, but not by a factor of two. A Planar Sensor Antenna response would be of the form:

Sensor Measurement = Product Dielectric * (Mass)Kw

where: Mass = weight, density, thickness etc. Kw = coefficient determined by antenna geometry (less than 1)

The value of Kw coefficient will depend upon antenna geometry, product presentation and form of mass measurement e.g. thickness, weight etc. To determine Kw, a constant moisture product of varying mass is presented to Sensor. A graph of log (Sensor response) vs. log (mass) must be plotted. Kw is given by the slope of this line (see Figure 14).

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The product dielectric is coupled to the antenna via an interface such as air. In some cases, direct contact may be made, or a fixed interface such as a Teflon or Ceramic window may isolate the Sensor from the product. The important thing is that the interface between product and Sensor, must remain constant in order for the interface dielectric to be cancelled out of the product measurement. In the case of direct contact or a window, this would be the case. If an air gap exists between product and Sensor and the air gap distance varies, due to mechanical vibration or board bounce, the total dielectric for the measurement will change. If the gap can be measured, it can be compensated.

If the antenna were a point source, then the RF energy would decrease according to the inverse square law and a simple compensation based upon the square of the distance would be possible. In practice the antenna is a finite width radiator producing a more complex relationship. It is further complicated by field distortion through the product.

Instrument

Mass

Figure 14: Plots of Sensor Measurement vs. Product Mass

Kw = log(y)/log(x)

log (Instrument)

log (Mass)

Figure 13 shows the typical field pattern emanating from a planar electrode, but this is somewhat idealized, as the field is actually distorted or refracted within the product. The amount of distortion is a function of product dielectric and is both density and moisture dependent. This distortion will also affect the field in the air gap and the distance relationship.

In practice, the product density usually remains fairly constant at a fixed point in the process, and the moisture similarly should not vary too greatly. If this is the case, distance may be corrected by an equation of the form:

Compensated Sensor = product dielectric * (distance + Kd)2

If moisture and density are uncontrolled such as raw material measurement, it is better to control or constrain the distance variation rather than try to compensate for it.

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The example to the left shows three Sensor measurements of differing moisture, at varying distances from the Sensor. No compensation is applied and an inverse relationship is apparent.

0 .25 .50 .75

Distance

. In this next example the same three Sensor measurements are

performed at varying distances. The Sensor has a compensation

equation:

Mc = Mu (D + 0.14)2

The offset coefficient Kd (.14) is determined by trial and error to obtain

0 .25 .50 .75

Distance

flattest response.

Figure 15: Plot of Sensor Measurement vs. Product Distance

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