SampleMaxMin (Sample When Maximum or Minimum Reached)
The SampleMaxMin instruction is used to sample one or more variable(s) when another variable (or range of variables) reaches its maximum or minimum for the defined output period.
Syntax
SampleMaxMin ( Reps, Source, DataType, DisableVar )
Example
The following program demonstrates using the SampleMaxMin instruction to output the wind direction when maximum and minimum wind speeds are sampled. In this demonstration program, artificial wind speeds and directions are generated with counters. To view the SampleMaxMin, run this program and then use software to collect and view data stored in Table1. The FieldNames instruction is used to avoid duplicate field names in the table.
'Declare Public Variables
Public WS_ms
Public WindDir
Units WS_ms=meters/second
Units WindDir=Degrees
'Define Data Table
DataTable(Table1,True,-1)
DataInterval(0,10,sec,0)
WindVector (1,WS_ms,WindDir,IEEE4,0,0,0,0)
FieldNames("WS_ms_S_WVT,WindDir_D1_WVT,WindDir_SD1_WVT")
Maximum (1,WS_ms,FP2,False,False)
SampleMaxMin (1,WindDir,FP2,False)
FieldNames("WindDir_smpMax") 'duplicate WindDir_SMM field name without this
Minimum (1,WS_ms,FP2,False,False)
SampleMaxMin (1,WindDir,FP2,False)
FieldNames("WindDir_smpMin") 'duplicate WindDir_SMM field name without this
EndTable
'Main Program
BeginProg
Scan(1,Sec,1,0)
'For demonstration, create some fake windspeed and wind direction values:
WS_ms=WS_ms+=1 'counter to generate wind speed
WindDir = WindDir+60 'counter to generate wind direction
If WindDir = 360 Then WindDir = 0 'reset wind direction
'Call Data Tables and Store Data
CallTable(Table1
NextScan
EndProg
Remarks
The SampleMaxMin instruction is placed inside a DataTable declaration, following the Maximum or Minimum instruction used as the basis for the output of this instruction. When the Repetitions parameter for the Maximum or Minimum instruction is greater than 1, SampleMaxMin samples whenever a new maximum or minimum occurs in any of the variables in the Maximum/Minimum source array.
Parameters
Reps (Repetitions)
The number of repetitions for the measurement or instruction.
Type: Constant integer (or expression that evaluates as a constant).
For the SampleMaxMin instruction, the Reps are the number of variables to sample when a maximum or minimum is reached. If the Reps parameter is greater than 1, an array must be specified for Source. If not, a Variable Out of Bounds error is returned when the program is compiled.
Source
The name of the Variable that is the input for the instruction. Right-click the parameter to display a list of defined variables.
Type: Variable
For the SampleMaxMin instruction, the Source is the name of the variable or variable array that is sampled when a new maximum or minimum occurs for the preceding Maximum or Minimum instruction.
Source may also be an expression. The resulting fieldname is AnonymousN, where N is an incrementing number assigned to each output value entered as an expression. The FieldNames instruction can then be used to change AnonymousN to a more appropriate fieldname; for example,
Sample (1,PTemp*1.8+32,FP2)
FieldNames("PTempDegFSample:Sample Panel Temp in degrees F")
DataType
A code to select the data storage format. Right-click the parameter to display a list.
| Name | Description |
|---|---|
| IEEE4 | IEEE four-byte floating point (IEEE 754 std). IEEE4 can also be specified using the keyword FLOAT. |
| FP2 | Campbell Scientific two-byte floating point. |
| IEEE8 | IEEE eight-byte floating point (double) |
Additional data types are available. However, not all data types are suitable for all output instructions, so they should be used with care.
| Name | Description |
|---|---|
| String | ASCII string; size defined by program |
| Boolean | 0 = False; -1 = True |
| BOOL8 | 1-byte Boolean value |
| Long | 32-bit long integer, ranging from -2,147,483,648 to +2,147,483,647 |
| NSEC | 8-byte time stamp format |
| UINT1 | One-byte unsigned integer |
| UINT2 | Two-byte unsigned integer |
| UINT4 | Four-byte unsigned integer |
UINT1: Holds an 8-bit unsigned integer (a number in the range of 0 - 32,767, where NAN values are stored as 0). The program should be written to check for values outside the range. This data type is an efficient means of storing 8-bit integers since it requires only one byte of memory in a data table. Floating point values are converted to UINT1 as if the INT function were used.
UINT2: Holds a 16-bit unsigned integer (a number in the range of 0 - 65535, where NAN values are stored as 0). The program should be written to check for values outside the range. This data type is an efficient means of storing 16-bit integers since it requires only two bytes of memory in a data table. Floating point values are converted to UINT2 as if the INT function were used.
UINT4: Holds a 32-bit unsigned integer (a number in the range of 0 to 4,294,967,295).
Long: Sets the output to a 32-bit long integer, ranging from -2,147,483,648 to +2,147,483,647 (31 bits plus the sign bit). There are two possible reasons a user would use this format: (1) speed, since the OS can do math on integers faster than with floats, and (2) resolution, since the Long has 31 bits compared to the 24-bits in the IEEE4. However, in most instances it is not suitable for output since any fractional portion of the value is lost.
BOOL8: Used to store variables that hold bits (0 or 1) of information. These values are shown in LoggerNet or other datalogger software as an array of eight Boolean values (each element in the array represents one bit). This data type uses less space than normal 32-bit values. Any reps stored must be divisible by two, since an odd number of bytes cannot be stored in a data table. When converting from a Long or a Float to a BOOL8, only the least significant 8 bits are used.
NSEC: An 8-byte time stamp format (4 bytes of seconds since 1990, 4 bytes of nanoseconds into the second) used when the variable being sampled is the result of the RealTime instruction or when the variable is a Long storing time since 1990 (for instance, when using TableName.TimeStamp). If the variable array is dimensioned to 7, the values stored will be year, month, day of year, hour, minutes, seconds, and milliseconds. The variable array must be declared as a Float or Long. If the variable array is dimensioned to two and declared as a Long, the instruction assumes that the first element holds seconds since 1990 and the second element holds microseconds into the second. If the source is a single variable dimensioned as a Long, the instruction assumes that the variable holds seconds since 1990 and the microseconds into the second is 0. In this instance, the value stored is a standard datalogger timestamp rather than the number of seconds since January 1990.
Type: Constant (or expression that evaluates as a constant)
DisableVar
A Constant, Variable, or Expression that is used to determine whether the current measurement is included in the output saved to the DataTable. Right-click the parameter to display a list.
- 0 = Process current measurement
- Non-zero = Do not process current measurement.
NOTE: For all instructions except Totalize, if the disable variable is true over the entire output interval, NAN Not a number. A data word indicating a measurement or processing error. Voltage overrange, SDI-12 sensor error, and undefined mathematical results can produce NAN. will be stored. For Totalize, if the disable variable is true over the entire output interval, 0 will be stored
See also Multipliers, Offsets, and Disable Variables with Repetitions.
Type: Constant, Variable, Expression