TECHNICAL NOTE - DT6

The purpose of the fourth difference is to enhance general disturbances or noise in real-time which will aid in the identifying of a true signal and the quality of data. The application is intended mainly for magnetometer data, although it can be applied to any ASCII data. For reference, see for example [1].

To implement the routine, the user should first be familiar with the following pseudo-channel documentation in the User's Guide:
 

5.3.5       Pseudo Channel Introduction

5.20.2     Menu for defining the data source of a pseudo-channel

5.28.3     Menu for the allocating of the pseudo-traces on the GR33A

5.28.4     Menu item for defining the data type or assigning the 4th difference routine to a data source   

The following procedures can be followed:

1. Define the data source of a pseudo-channel (Section 5.20.2) with the use of Named Variables and Extensions, or by User Defined Variables. This menu allows for the defining of up to ten pseudo-traces.
2. Proceed to the Analog #2 menu and assign which of the GR33A channels will be pseudo-traces (Section 5.28.3).
3. While in the Analog #2 menu, the data type of each pseudo-trace must be defined (Section 5.28.4). For this application note, the user would select 'ASC-4th DIFF.' for each of the pseudo-traces, recalling that up to a maximum of three channels may be defined utilizing the 4th difference routine.
4. The 'Compile Item List' of the Data List Configuration menu (Section 5.12) must have 'PSEUDO' inserted in the list.
5. Finally, the Named Routine 'TRACE' (Table 5-4) must be inserted just before TXGRB or TXGRS in the appropriate task list, (e.g. CHART,TRACE,TXGRB,SAMPLE.)

When a trace is derived from data, it is treated as a 32 bit number, regardless of the number of digits in the data (ignoring sign and decimal point). Any number of digits may be defined as well as the displacement on the chart in volts per cm.

The following is an example of pseudo-traces derived from an input to the BCD Module:
 

Digit Number		1	2	3	4	5	6	7	8	9	10	11
BCDB1		5	7	6	5	7	.	3	7	8	-	-		Example 1
		5	7	6	5	7	.	3	-	-	-	-		Example 2
		5	7	6	5	7	-	-	-	-	-	-		Example 3

Defining the above examples as pseudo-traces would be as follows:
 

Example 1:	BCDB1_0_8	The value used for evaluation is equivalent to 5.7657378.
Example 2:	BCDB1_0_6	The value used for evaluation is equivalent to 5.7657300.
Example 3:	BCDB1_0_5	The value used for evaluation is equivalent to 5.7657000.

If more resolution is required from Examples 2 and 3, the data will require leading zeros.
This can be accomplished by using the 'MOVE' Named Routine (Table 5-4) to an unused buffer area, and then defining the pseudo-trace.

GR33A SENSITIVITY SETTINGS

To set the recorder sensitivity in terms of gammas per cm, the following expression can be used:

where

V_o is the voltage out for the signal of data input,
n is the number of digits to the left of the decimal point,
N is the value of the signal or data input.

To obtain the sensitivity setting on the GR33A for 1 gamma per cm, use the following:

where

S is the sensitivity setting of the GR33A in volts/cm (or volts/inch),
Vo is the voltage output for 1 gamma from above,
d is the displacement on the GR33A in cm (or inches)