Geokon 8020-42CPR User manual

Installation Instructions
Model 8020-42CPR
Single Coil Autoresonant Adapter
4-20Ma Output
No part of this instruction manual may be reproduced, by any means, without the written consent of Geokon, Inc.
The information contained herein is believed to be accurate and reliable. However, Geokon, Inc. assumes no responsibility for
errors, omissions, or misinterpretation. The information herein is subject to change without notification.
Copyright © 2007-2018 by Geokon, Inc.
(Rev F, 08/23/2018)

Warranty Statement
Geokon, Inc. warrants its products to be free of defects in materials and workmanship, under
normal use and service for a period of 13 months from date of purchase. If the unit should
malfunction, it must be returned to the factory for evaluation, freight prepaid. Upon examination
by Geokon, if the unit is found to be defective, it will be repaired or replaced at no charge.
However, the WARRANTY is VOID if the unit shows evidence of having been tampered with
or shows evidence of being damaged as a result of excessive corrosion or current, heat, moisture
or vibration, improper specification, misapplication, misuse or other operating conditions outside
of Geokon's control. Components which wear or which are damaged by misuse are not
warranted. This includes fuses and batteries.
Geokon manufactures scientific instruments whose misuse is potentially dangerous. The
instruments are intended to be installed and used only by qualified personnel. There are no
warranties except as stated herein. There are no other warranties, expressed or implied, including
but not limited to the implied warranties of merchantability and of fitness for a particular
purpose. Geokon, Inc. is not responsible for any damages or losses caused to other equipment,
whether direct, indirect, incidental, special or consequential which the purchaser may experience
as a result of the installation or use of the product. The buyer's sole remedy for any breach of this
agreement by Geokon, Inc. or any breach of any warranty by Geokon, Inc. shall not exceed the
purchase price paid by the purchaser to Geokon, Inc. for the unit or units, or equipment directly
affected by such breach. Under no circumstances will Geokon reimburse the claimant for loss
incurred in removing and/or reinstalling equipment.
Every precaution for accuracy has been taken in the preparation of manuals and/or software,
however, Geokon, Inc. neither assumes responsibility for any omissions or errors that may
appear nor assumes liability for any damages or losses that result from the use of the products in
accordance with the information contained in the manual or software.

TABLE of CONTENTS
1. INTRODUCTION .................................................................................................................................................. 1
2. CONNECTIONS..................................................................................................................................................... 2
3. CONFIGURATIONS ............................................................................................................................................. 3
3.1 MICRO-10 DATALOGGER .................................................................................................................................... 3
3.2 GENERIC DATALOGGER CONFIGURATION........................................................................................................... 3
3.3. STAND ALONE CONFIGURATION ........................................................................................................................ 4
6. OUTPUT TO DIGITS CONVERSION................................................................................................................ 5
APPENDIX A. SPECIFICATIONS.......................................................................................................................... 6
FIGURES
FIGURE 1-BLOCK DIAGRAM......................................................................................................................................... 1
FIGURE 2-INTERNAL JUMPER SETTINGS FOR MICRO-10 CONFIGURATION ................................................................... 3
FIGURE 3-INTERNAL JUMPER SETTINGS FOR GENERIC DATALOGGER CONFIGURATION .............................................. 4
FIGURE 4-INTERNAL JUMPER SETTINGS FOR STAND ALONE CONFIGURATION............................................................. 4
TABLES
TABLE 1-CONNECTOR/SIGNAL DESCRIPTION............................................................................................................... 2
TABLE 2-SPECIFICATIONS ............................................................................................................................................ 6
EQUATIONS
EQUATION 1-CONVERT 4-20MAOUTPUT TO DIGITS.................................................................................................... 5

1
LPF
φ
1
φ2
VCO
Instrumentation
Amplifier
and
Schmitt Trigger
Phase Comparator
Output Buffer
VW Gage
Coil
Microprocessor
V+
1. INTRODUCTION
The Geokon 8020-42CPR is a device that allows single coil vibrating wire gages to be driven in
the “Autoresonant” mode, instead of the standard “Pluck and Read” mode, resulting in a greater
dynamic range (up to 20Hz). The benefits of Autoresonant vs. Pluck and Read topologies are
many, including greater reading stability and wider dynamic bandwidth. In addition, since there
is no asynchronous swept frequency or pulse pluck excitation to interfere with the vibrating wire
signal, there is the ability to read the gage frequency with a general-purpose frequency counter or
low cost datalogger, instead of a complex dedicated readout device or datalogger. In addition to
the gage frequency output, the 8020-42CPR also provides two 4-20mA signals that are
proportional to “digits” (frequency²). These 4-20mA outputs are factory set for the range of 2250
digits (1500Hz – 20mA) to 12250 digits (3500Hz - 4mA), but may be adjusted for other ranges.
One of the 4-20mA outputs is a non-isolated current source (I_out, / I_out). The other 4-20mA
output (LOOP_+, LOOP_-) is a current sink designed to be used in applications that require an
isolated controller. Typically, the 4-20mA output is adjusted to cover the full range span of a
single transducer.
Historically, autoresonant vibrating wire gages have employed two coils. The first is the
Transmit (excitation) coil that provides a phase synchronous pulse (pluck) to maintain
oscillation, while the second is the Receive (reading) coil that recovers the vibrating wire signal.
The two-coil approach, while dependable, adds to the cost and imposes a considerable
mechanical limitation to the design and construction of the gage. Since the SCA is designed to
operate as a “transceiver” using only one coil, these limitations are eliminated while providing
the benefits of the autoresonant mode.
Figure 1 - Block Diagram
Frequency
Output
Enable
PLL_OUT
VCO_HOLD
T/R
Switch

2
2. CONNECTIONS
Connector
Position
Signal
Name
Signal
Description
Type Level (typ.)
1 FOUT Vibrating Wire Gage Frequency Output 5Vpp
2 FOUT_ATT Vibrating Wire Gage Frequency - Attenuated Output 200mVpp
3 LOOP+ Isolated current loop + input (loop power) Power +10 to +30VDC
4 LOOP- Isolated current loop output Output Load dependent
5 DAS GND Power ground for 24V option Ground 0V
6 +12V +12V Power Supply input Power 6-15VDC
7 GND Ground Power 0V
8 /I_OUT Ground return for 4-20mA signal Power 0V
9 I_OUT 4-20mA source Output 4-20mA
10 C+ VW coil + Input 1mVpp
11 C- VW coil - Input 1mVpp
12 CR10EX Excitation (Micro-10 configuration) Input TTL/CMOS (EX)
13 CR10EN Enable (Micro-10 configuration) Input TTL/CMOS (C1.C7)
14 CR10CLK
Clock (Micro-10 configuration)
Enable (Generic Datalogger configuration)
Input TTL/CMOS (C8)
15 GND Ground Ground 0V
Table 1 - Connector/Signal Description
NOTE: Because the 8020-42 requires each vibrating wire gage to have its own pair of twisted
leads, the 8020-42 is not compatible with Geokon models 4900 (VW Load Cell) and 4350-3
(Biaxial Stressmeter).

3
3. CONFIGURATIONS
3.1 Micro-10 Datalogger
The 8020-42CPR can be incorporated as the vibrating wire interface in a Micro-10 Datalogger
system, taking the place of the Campbell Scientific Inc. AVW-1. In order to configure the 8020-
42CPR for the Micro-10 Datalogger, internal jumpers JP1, JP2 and JP3 must be set across pins
one and two. Remove the cover of the 8020-42 and set the jumpers:
JP1 JP2 JP3
Figure 2 - Internal Jumper Settings for Micro-10 Configuration
Between readings, the 8020-42CPR will be “asleep”, drawing approximately 20µA from the 12V
system battery.
When it is time to take a reading, the datalogger will set C1..C7 (CR10EN) high in order to
enable the respective multiplexer, and the individual channels are clocked by pulsing C8
(CR10CLK) high.
When “CR10EN” and “CR10CLK” are both high, the 8020-42CPR will wake up and wait for
the swept frequency excitation signal to appear at EX. The 8020-42CPR will track and apply this
swept frequency to the VW gage. Once the swept frequency is complete, the 8020-42CPR will
lock onto the returned VW signal and maintain excitation by applying one excitation pulse for
every 16 cycles of VW frequency. The VW frequency is provided as both a 200mv(pp) signal at
FOUT_ATT (connector position two), and as a 5v(pp) 50Ωoutput at FOUT (connector position
one).
It is helpful to add a small amount of delay ( ≈0.5 Sec. ) from the time that the swept frequency
excitation ends and the time that the reading is taken. MultiLogger software, ver. 1.4.0 and above
provides this delay when selecting a gage type that has the letters sca included within it, i.e.,
4500sca, 4700sca etc.
3.2 Generic Datalogger Configuration
The 8020-42CPR can be incorporated as the vibrating wire interface for any datalogger that is
capable of reading a frequency input or a 4-20mA current input and has the ability to output a
single 5V CMOS level control signal. In order to configure the 8020-42CPR for a generic
Datalogger, internal jumpers JP1 and JP3 must be set across pins one and two, while JP2 is set
across pins two and three. Remove the cover of the 8020-42CPR and set the jumpers:
Pin 1
Pin 2
Pin 3

4
JP1 JP2 JP3
Figure 3 - Internal Jumper Settings for Generic Datalogger Configuration
Between readings, the 8020-42CPR will be “asleep”, drawing approximately 20µA from the 12V
system battery.
When it is time to take a reading, the datalogger will set its control signal, which should be
connected to CR10CLK, high. When CR10CLK goes high, the 8020-42CPR will generate a 400-
4500 Hz swept frequency pluck in order to excite the VW gage. As with the Micro-10
configuration, once the swept frequency is complete, the 8020-42CPR will lock onto the returned
VW signal and maintain excitation by applying one excitation pulse for every 16 cycles of VW
frequency.
The 8020-42CPR will provide continuous VW frequency output until the CR10CLK control line
is brought low. At this time, the 8020-42CPR will go back to sleep
3.3. Stand Alone Configuration
When configured in the Stand Alone mode, the 8020-42CPR will provide continuous excitation
and frequency output from a single Vibrating Wire gage. All that is needed is a 12V (nominal)
voltage source and a frequency counter to read the VW frequency. In order to configure the
8020-42CPR for Stand Alone mode, internal jumpers JP1, JP2 and JP3 must be set across pins
two and three. Remove the cover of the 8020-42CPR and set the jumpers:
JP1 JP2 JP3
Figure 4 - Internal Jumper Settings for Stand Alone Configuration
Pin 1
Pin 2
Pin 3
Pin 1
Pin 2
Pin 3

5
6. OUTPUT TO DIGITS CONVERSION
Use the following formula to convert the 4-20mA output signal to “Digits”:
Digits = 12250 - [625 x (mA-4)]
Equation 1 - Convert 4-20mA Output to Digits
Where;
mA = 8020-42CPR 4-20mA output signal
For example:
If the 8020-42CPR is outputting a 4-20mA current of 12mA then:
Digits = 12250 – [625 x (12 – 4)]
Digits = 12250 – [625 x 8]
Digits = 12250 – 5000
Digits = 7250

6
APPENDIX A. SPECIFICATIONS
POWER
Power Requirements: 6-15 VDC (12V nominal)
Current Consumption:
Sleep: 30 µA (max.), 20µA (typ.)
Plucking: 50 mA peak
PLL locked: 30 mA (max.), 22 mA (typ.)
50 mA (max) with 4-20mA
Iout
PLL Capture Range: 1200 – 4000 Hz
PLL Lock Range: 1150 – 4500 Hz
Internally Generated Fsweep:
Frequency (start): 400 Hz
Frequency (end): 4500 Hz
Sweep Duration: 750 mSec
Sweep Shape: Linear
Frequency Outputs:
FOUT_ATT: 200mVpp 1kΩAC coupled
FOUT: 5Vpp 50ΩAC coupled
Control Inputs:
CR10EN: 5V CMOS
CR10CLK: 5V CMOS
EX: 5V CMOS: VW excitation
ENVIRONMENTAL
Temperature range: 0 - 70 °C
Table 2 - Specifications