Hamilton Electronics EPHUM011 manual Defining a Constant Current Output for Testing

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

Attention:

When assigning measurement values to 4-20 mA analog output by using register 4378 / 4506, you need to consider the following:

The PMC you have mapped to AO1 / AO2 (register 4364 / 4492)

The physical unit currently in use for the selected PMC (register 2090 for PMC1 (pH) and

register 2410 for PMC6 (temperature).

Therefore, when the operator redefines one of the register 4364 / 4492, 2090 / 2410, the definitions of the register 4378 / 4506 should be reviewed. If not, the current output at the 4-20 mA interfaces may be wrong.

Note:

The physical unit of the analog output corresponds always to the unit that is set for the selected PMC (register 2090 for PMC1 or register 2410 for PMC6). Accordingly, not only the pH value is selectable at the 4-20 mA interface, but also mV values, degrees centigrade or Kelvin.

Example:

Register 4364 is set to 1 (PMC1 is mapped to AO1).

Register 2090 is set to 0x1000 (the unit “pH”is assigned to PMC1). Register 4378 is set to 2 and 10 (4 mA = pH 2, 20 mA = pH 10).

The sensor reads currently pH 4, the output at the 4-20 mA is accordingly 8 mA.

The operator now re-assigns register 2090 to the value of 0x200000 (unit = mV), but does not modify all other registers. The sensor is still at pH 4 and reads now +170 mV. At the analog output, as 20 mA is programmed to a value of 10 by register 4378, the current will go to the maximum value of 20 mA.

This will generate an interface warning “4-20 mA current set point not met”.

2.4.5.7Defining a Constant Current Output for Testing

Note:

For constant current output, the AO1 / AO2 must be set to analog interface mode 0x01:

Start	Number of	Reg1 / Reg2	Modbus	Read	Write
register	registers		function code	access	access
4384	2	Constant current output value for	3, 4, 16	U/A/S	S
		AO1 [mA]
4512	2	Constant current output value for	3, 4, 16	U/A/S	S
		AO2 [mA]

Figure 2.4.5.7.1: Definition of register 4384 / 4512.

Command: Fixed value AO1		Modbus address: 4384	Length: 2	Type: 3	Read
Parameter:	Fixed value [mA]
Format:	Float
Value:	10

Figure 2.4.5.7.2: Example to read the constant current output in mode 0x01 for AO1. It is set to 10 mA.

624300/01 page 15 / 67