Hamilton Electronics EPHUM011 manual Available Calibration Points

pH ARC Sensors Modbus RTU Programmer’s Manual (EPHUM011)

2.7Calibration

2.7.1 Available Calibration Points

In register 5120, the available number of Calibration Points (CP) for Primary Measurement Channel 1 (PMC1) is defined. 8 individual CP are theoretically possible.

Start	Number of	Reg1 / Reg2	Modbus	Read	Write
register	registers	(bitwise defined)	function code	access	access
5120	2	Available number of CP for PMC1	3, 4	U/A/S	none
		(see figure 2.7.1.2)

Figure 2.7.1.1: Definition of register 5120.
Bit #		Hex value		Description		Definition in ARC Sensors
0	(LSB)	0x01		CP1		Calibration Point 1
1		0x02		CP2		Calibration Point 2
2		0x04		CP3		not available
…		…		…		not available
5		0x20		CP6		Product Calibration
6		0x40		CP7		not available
7	(MSB)	0x80		CP8		not available
Figure 2.7.1.2:		Bitwise definition	of CP1 to CP8.
Command: Available cali points					Modbus address: 5120		Length: 2	Type: 3	Read
Parameter:		Points
Format:		Hex
Value:		0x23

Figure 2.7.1.3: Example to read the available CPs. 0x23 = 0x01 (CP1) + 0x02 (CP2) + 0x20 (CP6).
			Standard Calibration at 2 calibration points
	200
ref [mV]	150					CP1
	100
vs.
glass	50								CP2
	0
potential
	-50
electrical	-100
	-150
	-200
	0	1	2	3	4	5	6	7	8	9	10	11	12	13	14
								pH value

Figure 2.7.1.4: pH ARC Sensors allow 3 calibration points:

CP1 and CP2 are used for standard calibration (shown in this figure).

The product calibration CP6 is used to adjust the standard calibration function to specific process conditions (the effect of CP6 is shown in Figure 2.7.3.2.1).

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