Hach pHD sc
Digital differential pH or ORP sensor, read through a Hach sc controller with a Modbus RS485 module.
The Hach pHD sc is a digital differential pH or ORP sensor that measures process water, such as irrigation and drain water in greenhouses, and connects to a Hach sc controller. This Modbus RTU template reads pH or ORP, temperature, electrode impedances and the error and status words, and lets you write sensor settings such as the temperature element and impedance limits from ModbusCloud.
- Protocol
- Modbus RTU
- Connection
- RS485, 19200 baud
- Registers
- 68, read and write
- Brand
- Hach
- Key readings
- pH or ORP · Temperature · Electrode impedance · Sensor signal · Error and status word · Calibration slope and offset
- Available commands
- Sensor type pH or ORP · Temperature element · Calibration buffer set · Impedance limits · Log intervals
- Compatible models
- pHD sc digital differential pH sensor (DPD) · pHD sc digital differential ORP sensor (DRD)
- Last updated
Registers (68)
68 read, 41 write
| Name | Unit | Access | Address (Hidden until you enter your email) | Function (hidden) | Type (hidden) |
|---|---|---|---|---|---|
| pH or ORP Value | Read | ||||
| Temperature | °C | Read | |||
| Sensor Signal | mV | Read and write | |||
| Active Electrode Impedance | Read and write | ||||
| Reference Electrode Impedance | Read and write | ||||
| pH Slope | Read and write | ||||
| pH Offset | Read and write | ||||
| ORP Offset | mV | Read and write | |||
| Sensor ADC Counts | Read | ||||
| Temperature ADC Counts | Read | ||||
| Active Impedance Counts | Read | ||||
| Reference Impedance Counts | Read | ||||
| Electrode Status | Read | ||||
| Sensor Days | d | Read and write | |||
| Electrode Days | d | Read and write | |||
| Last Calibration Date | Read | ||||
| Classified Error Word | Read | ||||
| Classified Status Word | Read | ||||
| Measurement Type | Read and write | ||||
| Temperature Units | Read and write | ||||
| pH Display Format | Read and write | ||||
| Tagged pH Format | Read and write | ||||
| Filter Time | s | Read and write | |||
| Temperature Element | Read and write | ||||
| Manual Temperature Value | °C | Read and write | |||
| pH Buffer Set | Read and write | ||||
| Pure Water Compensation Type | Read and write | ||||
| Pure Water Compensation Slope | Read and write | ||||
| Reject Frequency | Read and write | ||||
| Impedance Check | Read and write | ||||
| Active Impedance Low Limit | Read and write | ||||
| Active Impedance High Limit | Read and write | ||||
| Reference Impedance Low Limit | Read and write | ||||
| Reference Impedance High Limit | Read and write | ||||
| Impedance Active Correction | Read and write | ||||
| Impedance Reference Correction | Read and write | ||||
| Calibration Warning Days | d | Read and write | |||
| Sensor Warning Days | d | Read and write | |||
| Sensor Log Interval | Read and write | ||||
| Temperature Log Interval | Read and write | ||||
| Output Mode | Read and write | ||||
| Calibration Leave | Read and write | ||||
| Calibration Abort | Read and write | ||||
| Calibration Edit Value Tag | Read and write | ||||
| Calibration Edit Value | Read and write | ||||
| Calibration Code | Read and write | ||||
| Edit Temperature Value | Read and write | ||||
| Edit Temperature Minimum | Read | ||||
| Edit Temperature Maximum | Read | ||||
| Sensor Measurement Tag | Read | ||||
| Temperature Measurement Tag | Read | ||||
| Manual Temperature Tag | Read and write | ||||
| Function Code | Read and write | ||||
| Next State | Read | ||||
| Sensor Name | Read and write | ||||
| Sensor Name Long | Read | ||||
| Serial Number | Read | ||||
| Software Version | Read | ||||
| Software Version 1 | Read | ||||
| Software Version 2 | Read | ||||
| Boot Version | Read | ||||
| Sensor Type | Read | ||||
| Device Driver | Read | ||||
| Device Driver 1 | Read | ||||
| Device Driver 2 | Read | ||||
| Device Driver 3 | Read | ||||
| Device Driver 4 | Read | ||||
| Production Date | Read and write |
Loading registers…
Send your device list
If a device is not in the library yet, we build the template for free as soon as we have the register data.
Use cases
- Show pH and temperature of irrigation or drain water on a dashboard next to EC and dissolved oxygen.
- Get an email or webhook alert when the pH goes above or below the limits you set for the nutrient solution.
- Alert on an error word that is not 0, so a failed calibration or hardware fault reaches you right away.
- Follow the active and reference electrode impedance over months to plan salt bridge and sensor replacement.
- Keep 365 days of pH history to compare dosing changes, water sources and seasons.
Installation
Fit the Modbus RS232/RS485 module in the Hach sc200 or SC4500 controller and set its switches to RS485, with termination on at the end of the bus.
Wire RS485 A and B of the module to A and B of the ModbusCloud Gateway and terminate both ends of the bus.
In the controller's Modbus settings, set or note the Modbus address of the pHD sc. Keep 19200 baud, RTU, no parity, 1 stop bit and data order Little Endian.
In ModbusCloud, add a Modbus device with the address of the sensor and the same serial settings, then import this template.
Check that pH or ORP and temperature match the controller display.
Things to watch for
The sensor does not answer. What should I check?
Every sensor answers on its own Modbus address, not on the address of the controller or the module. Check the address of this sensor in the controller's Modbus settings, the serial settings (19200 baud, no parity, 1 stop bit by default), that switch 4 on the module selects RS485 and that A and B are not swapped. The template needs the RS485 module; it does not work over SC4500 Modbus TCP.
pH and temperature show huge or tiny numbers. Why?
The template expects the factory data order of the Modbus module, Little Endian. When the data order in the controller is set to Big Endian, the two halves of every value are swapped. Set the data order back to Little Endian.
Is the main value pH or mV?
The same register holds pH on a pH sensor and mV on an ORP sensor, depending on the sensor type set in the controller. The template shows it without a unit so it fits both. Temperature is in °C unless the sensor is set to °F.
Can I read the sensor through an SC1000 controller?
Yes, with the SC1000 Modbus RS485 card and virtual slaves switched on. Each sensor then answers on its own address, counting up from the address of the configured slave. The template is set for the factory word order of the sc200 and SC4500 module; scrambled values on an SC1000 point to a different word order.
Can I write settings from ModbusCloud safely?
A write changes the sensor configuration directly, the same as the controller menu. Read the current value first, change one setting at a time and leave the calibration and menu registers alone while someone works on the controller. Register writing is off per gateway until you request it.
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