DTS Software Gain Calculations

Purpose

The purpose of this article is to supply information relating to the Gain Calculations and Settings used in DTS Software Suites with respect to SLICE MICRO/NANO/IP68, SLICE6 and SLICE6 AIR.  The attached spreadsheet provides quick calculations and guidance on settings for a desired gain value.

Background

DTS DAS Gain Architecture

Available gain ranges in DTS DAS systems are dictated by the Gain Architecture circuitry built into the Bridge input channels.  The basic Gain Architecture can be seen in the following diagram:

To see a pictorial representation of the channel architecture for each DAS type, see these articles:

• SLICE MICRO/NANO/IP68:  User's Manual - SLICE MICRO/NANO (p. 48) 

• SLICE6:  SLICE6 - Sensor Connections Diagrams (p. 2)

• SLICE6 AIR:  SLICE6 AIR Making Connections (p. 9)

Possible Gain Ranges

When configured like the above diagram, the gain architecture represents a cascading amplifier configuration.  To determine the resultant gain of a cascading amplifier configuration, you would take the product of all amplifier gains in the system:

Based on this architecture above, DTS DAS have 16 possible gain settings ranging from a value of 1 to a value of 1280.  A full list of the available gain values for a channel based on this architecture can be found in the attached spreadsheet on the 'Possible Gain Stages' tab.

Possible Gain Stages Worksheet

This worksheet provides a list of allowable gains for SLICE Bridge and IEPE channels.  As previously mentioned, there are 16 gain options for the SLICE Bridge and SLICE6 AIR IEPE channels and there are 2 settings available for all other SLICE IEPE channels.

How Does DTS Software Determine the Gain Setting?

When selecting the gain for a specific channel, DTS software takes the values located in several user-configurable fields in the Sensor Settings into account: 

• Proportional
• Sensitivity
• Desired Range

For Proportional sensors, the Excitation field is also used.

The software also takes into account a Range Overhead or Headroom value.  The default recommended value for this setting is 20%.

• For SLICEWare, the value is located in the SLICEWare.exe.config file inside the software version folder in the Install Location:
  
• For DataPRO, the value is user-configurable in the Test options tab under System Settings.  The value is called Range overhead factor (%). 
  
  • Please note, in DataPRO this value is represented as a factor, meaning that a 20% headroom would equal a factor of 120.  A headroom of 0 would be 100 and a headroom of 30% would be 130.

Gain Calculation Equations

The algorithm is based on the standard bipolar input range for the DAS:

• SLICE MICRO/NANO/IP68, SLICE6 = 2450 mV (2.5 V center)
• SLICE6 AIR = 2500 mV (2.5 V center)

The equations are as follows:

• For Proportional Sensors:
  
• For Non-Proportional Sensors:
  

As there are a finite number of gain options available, DTS Software uses the first gain value equal to or below the calculated value from the available options.  For example, if the ideal gain value would be 18, the options surrounding that would be 16 or 20, so the Software would select 16.  Thus, the actual range determined during diagnostics will always be at least the desired range plus the headroom percentage.

Using the Quick-Calculation Spreadsheet

The attached spreadsheet provides a set of quick-calculation tables that provide guidance on default gain settings based on sensor input values as well as guidance on setting sensor values to achieve a desired gain value.  There are two quick-calculation worksheets:  Bridge Gain Worksheet and IEPE Worksheet.  Dependent upon the type of sensor you are working with, you would use the associated worksheet.

Software Gain Selection Table

The Software Gain Selection table allows the user to enter their standard sensor settings into the Variables section and provides the default gain settings configured by the DTS Software for those settings.

Forced Gain Settings and Software Sensor Settings Tables

The Forced Gain Settings table allows the user to select a desired gain setting from the dropdown menu of allowable gains and then provides guidance on configuring the sensor settings in the DTS Software to apply the desired gain, via the values provided in the Software Sensor Settings table.

Please note, that there is no Forced Gain Settings table for IEPE sensors.  If you need help with this process, please submit a request to Technical Support and we will work with you to get you the settings you need.