GHM Delta OHM HD2156.1 User manual

Operating manual
Conductivity meters / pH meters /
thermometers
HD2156.1 – HD2156.2
www.deltaohm.com
English
Keep for future reference.
Companies / Brands of GHM

HD2156 - 2 - V2.5
CONTENTS
INTRODUCTION ............................................................................................................................................................ 3
KEYBOARD AND MENU DESCRIPTION .................................................................................................................. 8
PH MEASUREMENT .................................................................................................................................................... 16
AUTOMATIC OR MANUAL pH COMPENSATION .............................................................................................................. 16
PH ELECTRODE CALIBRATION ....................................................................................................................................... 17
Temperature characteristics of Delta OHM pH standard solutions ......................................................................... 20
CONDUCTIVITY MEASUREMENT .......................................................................................................................... 21
AUTOMATIC OR MANUAL CONDUCTIVITY COMPENSATION ........................................................................................... 22
CALIBRATION OF CONDUCTIVITY .................................................................................................................................. 23
Table of standard solution at 147S/cm, 1413S/cm, 12.88mS/cm and 111800mS/cm ........................................ 26
DIRECT INPUT INTO Pt100 AND Pt1000 TEMPERATURE PROBES .................................................................................... 27
How to measure ...................................................................................................................................................... 27
Instructions to connect the TP47 module for conductivity/temperature combined probes, 4-wire
Pt100 probes, and 2-wire Pt1000 probes ................................................................................................................. 27
WARNINGS AND OPERATING INSTRUCTIONS .................................................................................................. 31
NOTES ON THE USE OF THE pH ELECTRODES ................................................................................................................. 32
NOTES ON CONDUCTIVITY PROBES ................................................................................................................................ 32
INSTRUMENT SIGNALS AND FAULTS .................................................................................................................. 33
LOW BATTERY WARNING AND BATTERY REPLACEMENT ......................................................................... 35
INSTRUMENT STORAGE ........................................................................................................................................... 36
SERIAL INTERFACE AND USB ................................................................................................................................. 37
STORING AND TRANSFERRING DATA TO A PERSONAL COMPUTER ........................................................ 39
THE LOGGING FUNCTION - ONLY FOR HD2156.2 .......................................................................................................... 39
CLEARING THE MEMORY - ONLY FOR HD2156.2 ........................................................................................................... 39
THE PRINT FUNCTION .................................................................................................................................................. 40
CONNECTION TO A PC .............................................................................................................................................. 41
CONNECTION TO THE RS232C SERIAL PORT OF THE INSTRUMENT ................................................................................ 41
CONNECTION TO THE USB 2.0 PORT OF THE INSTRUMENT - ONLY FOR HD2156.2 ........................................................ 41
NOTES ABOUT WORKING AND OPERATIVE SAFETY ..................................................................................... 42
INSTRUMENT TECHNICAL CHARACTERISTICS .............................................................................................. 43
TECHNICAL DATA OF PROBES ............................................................................................................................. 47
pH ELECTRODES ....................................................................................................................................................... 47
2 AND 4-ELECTRODE CONDUCTIVITY PROBES ........................................................................................................... 47
Pt100 4-WIRE PROBES AND Pt1000 2-WIRE PROBES COMPLETE WITH TP47 MODULE .............................................. 48
ORDER CODES ............................................................................................................................................................. 49

HD2156 - 3 - V2.5
INTRODUCTION
The HD2156.1 and HD2156.2 are portable instruments with a large LCD display. They measure
pH, mV, redox potential (ORP), conductivity, liquid resistivity, total dissolved solids (TDS) and sa-
linity using combined 4-ring and 2-ring conductivity/temperature probes. Temperature only is
measured by Pt100 or Pt1000 immersion, penetration or contact probes.
The pH electrode calibration, as well as manual, can be carried out automatically on one, two or
three points and the calibration sequence can be chosen from a list of 13 buffers.
The probe calibration can be performed automatically in one or more of the 147S/cm, 1413S/cm,
12880S/cm or 111800S/cm conductivity calibration solutions.
The HD2156.2 instrument is a datalogger. It memorizes up to 20,000 sets of three measurements
composed of pH or mV, conductivity or resistivity or TDS or salinity and temperature: these data
can be transferred from the instrument connected to a PC via the RS232C serial port or USB 2.0
port. The storing interval, printing, and baud rate can be configured using the menu.
The HD2156.1 and HD2156.2 models are fitted with an RS232C serial port and can transfer the ac-
quired measurements to a PC or to a portable printer in real time.
Printing and, for the model HD2156.2, storing always include three parameters: temperature – pH
or mV – χ or Ω or TDS or g/l.
The Max, Min and Avg function calculates the maximum, minimum or average values.
Other functions include: the Auto-HOLD function and the automatic turning off which can also be
disabled.
The instruments have IP66 protection degree.
This manual describes the HD2156.1 and HD2156.2 models: if not otherwise specified, the de-
scription is intended to be applicable to both models.

HD2156 - 4 - V2.5
Conductivity meter – pH meter – Thermometer
HD2156.1

HD2156 - 5 - V2.5
HD2156.1
1. BNC connector for the pH/mV electrode.
2. 8-pole DIN45326 connector, input for combined 4-ring or 2-ring conductivity/temperature
probes, for direct 4-wire Pt100 temperature probes and 2-wire Pt1000 probes complete with
TP47 module.
3. External auxiliary power supply connector input (positive at centre).
4. Battery symbol: displays the battery charge level.
5. Function indicators.
6. Secondary display line.
7. CAL/ key: during normal operation starts the conductivity probe or pH electrode calibration;
in the menu, increases the current value.
8. FUNC/ENTER key: during normal operation displays the maximum (MAX), the minimum
(MIN) and the average (AVG) of current measurements; in the menu, confirms the current se-
lection. This updates the display measurement when the Auto-Hold function is enabled.
9. pH/mV-ESC key: changes the main variable measurement between pH and mV. In the menu,
confirms the current selection.
10. SERIAL key: starts and ends the data transfer to the serial communication port.
11. MENU key: allows access to and exit from the menu.
12. χ-Ω-TDS/ESC key: changes the main variable measurement between conductivity, resistivity,
total dissolved solids (TDS) and salinity. In the menu, cancels the operation in progress without
making changes.
13. °C/°F key: when the probe is not connected, allows manual modification of the temperature.
When the probe is connected, if this key is pressed twice, it changes the unit of temperature
measurement from degrees Celsius to Fahrenheit.
14. ON-OFF/AUTO-OFF key: turns the instrument on and off; when pressed together with the
CAL key, disables the automatic turn off.
15. pH electrode efficiency indicators.
16. MAX, MIN and AVG symbols.
17. Main display line.
18. Line for symbols and comments.
19. 8-pole MiniDin connector for RS232C. For the connection to PC (with cable HD2110CSNM or
C206) or printer (with cable HD2110CSNM).

HD2156 - 6 - V2.5
Conductivity meter – pH meter – Thermometer
HD2156.2

HD2156 - 7 - V2.5
HD2156.2
1. BNC connector for the pH/mV electrode.
2. 8-pole DIN45326 connector, input for combined 4-ring or 2-ring conductivity/temperature
probes, for direct 4-wire Pt100 temperature probes and 2-wire Pt1000 probes complete with
TP47 module.
3. External auxiliary power supply connector input (positive at centre).
4. Battery symbol: displays the battery charge level.
5. Function indicators.
6. Secondary display line.
7. CAL/ key: during normal operation starts the conductivity probe or pH electrode calibration;
in the menu, increases the current value.
8. FUNC/ENTER key: during normal operation displays the maximum (MAX), the minimum
(MIN) and the average (AVG) of current measurements; in the menu, confirms the current se-
lection. This updates the display measurement when the Auto-Hold function is enabled.
9. pH/mV-ESC key: changes the main variable measurement between pH and mV. In the menu,
confirms the current selection.
10. SERIAL/ERASE LOG key: starts and ends the data transfer to the serial communication port.
In the menu, clears the data contained in the instrument's memory.
11. LOG/DUMP LOG key: during normal operation, starts and ends the saving of the data in the
internal memory; in the menu, starts the data transfer from the instrument's memory to the PC.
12. Mini-USB type B connector for USB 2.0. For the connection to PC (with cable CP23).
13. MENU key: allows access to and exit from the menu.
14. χ-Ω-TDS/ESC key: changes the main variable measurement between conductivity, resistivity,
total dissolved solids (TDS) and salinity. In the menu, cancels the operation in progress without
making changes.
15. °C/°F key: when the probe is not connected, allows manual modification of the temperature.
When the probe is connected, if this key is pressed twice, it changes the unit of temperature
measurement from degrees Celsius to Fahrenheit.
16. ON-OFF/AUTO-OFF key: turns the instrument on and off; when pressed together with the
CAL key, disables the automatic turn off.
17. pH electrode efficiency indicators.
18. MAX, MIN and AVG symbols.
19. Main display line.
20. Line for symbols and comments.
21. 8-pole MiniDin connector for RS232C. For the connection to PC (with cable HD2110CSNM or
C206) or printer (with cable HD2110CSNM).

HD2156 - 8 - V2.5
KEYBOARD AND MENU DESCRIPTION
Foreword
The instrument keyboard is composed of single-function keys, like the MENU key, and double-
function keys such as the ON-OFF/Auto-OFF key.
In the double-keys, the function in the upper part is the "main function", while the one in the bottom
part is the "secondary function". When the instrument is in standard measurement mode, the main
function is active. In the menu or in conjunction with the FUNC key, the secondary function is ena-
bled.
The pressing of a key is accompanied by a short confirmation beep: a longer beep sounds if the
wrong key is pressed.
Each key specific function is described in detail below.
The following can be seen on the display at the same time:
1. pH (or mV) and temperature
2. conductivity (or resistivity or total dissolved solids or salinity) and temperature.
It is not possible to see pH (or mV) and conductivity at the same time: one measurement or
the other must be selected using the "pH/mV - " and "χ-Ω-TDS/ESC" keys. In direct print
and when logging three quantities are captured at the same time: pH/mV, conductivity and
temperature.
ON-OFF/Auto-OFF key
The instrument is turned on and off using the ON/OFF key. Turning on enables all display segments
for a few seconds, starts an auto-test, and displays the current values of cell constant (CELL) and
temperature coefficient  (ALPH). Finally, the instrument is set in standard working mode, dis-
playing the measurement which remained enabled at the last turning off in the main line, and the
temperature in the secondary line.
MIN
cm
min s
2
3
mµ
m
k
>>>
During turning on, should no probes be connected, the last manually-set temperature appears
in the secondary line. The unit of measurement symbol (°C or °F) starts blinking, and a letter
"m" meaning "manual" appears next to the battery symbol.
The probe's data are captured upon turning the instrument on: if the ERR message appears
in the secondary line, it is necessary to turn the instrument off and then on again.
Replace the probes when the instrument is off.

HD2156 - 9 - V2.5
+
Automatic turning off
The instrument has an AutoPowerOff function that automatically turns the instrument off after about
8 minutes if no key is pressed during the intervening time. The AutoPowerOff function can be disa-
bled by holding the CAL/ key pressed down when turning the instrument on: the battery symbol
will blink to remind the user that the instrument can only be turned off by pressing the <ON/OFF>
key.
The automatic turning off function is disabled when external power is used. On the other
hand, it cannot be disabled when the batteries are discharged.
FUNC/ENTER key
During normal measurement this enables the display and logging of the maximum (MAX), mini-
mum (MIN) and average (AVG) value of the pH, mV, conductivity, liquid resistivity, total dis-
solved solids, salinity and temperature measurements, updating them with the acquisition of new
samples. The acquisition frequency is once a second.
To switch from pH to mV, press the "pH/mV-" key. Use the χ-Ω-TDS/ESC key to switch from
conductivity to liquid resistivity, to total dissolved solids or to salinity.
In the menu, the ENTER key confirms the current parameter and then goes to the next one.
The MAX, MIN and AVG measurements remain in the memory until the instrument is on, even af-
ter exiting the calculation function. To reset the previous values and restart with a new measurement
session, press FUNC until the message "FUNC CLR" appears, then use the arrows to select YES
and confirm using ENTER.
According to settings in the "RCD Mode" menu item, the maximum, minimum and average
indications have different meanings: please see the description of this MENU key below.
Attention: the data captured using the Record function cannot be transferred to the PC.
CAL/ key
It increases the current parameter when used in the menu; when used in measurement mode, it starts
the displayed variable (pH or conductivity) calibration (please see the chapter dedicated to pH, page
17, and conductivity, page 23, calibration).
°C/°F key
When a probe with temperature sensor is connected, the key changes the unit of measurement from
degrees Celsius to Fahrenheit. The measured temperature value is used to compensate the pH or
conductivity measurement.
If the probe is not present, the compensation temperature must be entered manually: to manually
change the value shown in the display lower line, press °C/°F once. The temperature indicated starts

HD2156 - 10 - V2.5
blinking. While the display is blinking, it is possible to change the compensation temperature using
the arrows ( and ). Confirm using ENTER. The display stops blinking, and the temperature
displayed is used for compensation.
If the temperature probe is not present, to change the unit of measurement between °C and °F, it is
necessary to press twice the °C/°F key.
χ-Ω-TDS (conductivity - resistivity - total dissolved solids - salinity) / ESC key
Changes the main variable measurement between conductivity, resistivity, total dissolved solids
(TDS) and salinity. The selected parameter is used for display, printing, and logging.
In the menu, the key clears or cancels the active function (ESC).
Auto-HOLD function
The instrument has an Auto-Hold function, which can be set in the MENU, that "freezes" the meas-
urement automatically when it has been stable (within 1 digit) for over 10 seconds: the message
HOLD is displayed.
To perform a new measurement, it is necessary to press the FUNC/ENTER key.
The HOLD message starts blinking, while the display follows the actual measurement trend, until it
stabilizes again and the HOLD message remains still.
pH/mV -  key
Changes the main variable measurement between pH and mV. The selected parameter is used for
display, printing, and logging.
Auto-HOLD function
The instrument has an Auto-Hold function, which can be set in the MENU, that "freezes" the meas-
urement automatically when it has been stable (within 1 mV) for over 10 seconds: the message
HOLD is displayed.
To perform a new measurement, it is necessary to press the FUNC/ENTER key.
The HOLD message starts blinking, while the display follows the actual measurement trend, until it
stabilizes again and the HOLD message remains still.
NOTE: when the Auto-Hold function is enabled, the measurement in mV is disabled. To restore
the display in mV, disable the Auto-Hold function in the menu.
When used in the menu, it decreases the current variable value.
MENU Key
The first menu item is accessed by initially pressing on the MENU key; press ENTER to go to the
following items. To modify the item displayed, use the arrow keys ( and ). The current value is
confirmed by pressing the ENTER key and the display moves on to the next parameter. If pressing
ESC, the setting is cancelled.
To exit the menu, press the MENU key at any time.

HD2156 - 11 - V2.5
The menu items are listed in this order:
1) Management of memorized data (only HD2156.2): the message "LOG_DUMP_or_E-
RAS" (Transfer data or erase) is scrolled in the comment line. The center figure reports
the number of free memory pages (FREE). All memory data are permanently erased by
pressing SERIAL/EraseLOG. By pressing LOG/DumpLOG, the data transfer of the logged
data on the serial port is started: the "BAUD-RATE" must have previously been set to the
maximum value (please see the menu items described below and the paragraph "STORING
AND TRANSFERRING DATA TO A PERSONAL COMPUTER" on page 39).
2) Identifier of the sample being measured: it is an automatically increased progressive
number associated with the single PRINT function (print interval set to 0) for the printing
of labels. The index appears in the single sample printing together with date, time, conduc-
tivity (liquid resistivity, total dissolved solids or salinity) and temperature or pH (or mV)
measured values. This menu item allows the value of the first sample to be set: each time the
PRINT key is pressed, the identification ID in the printing is increased by 1 allowing pro-
gressive measurement of all measured samples. If the Auto-Hold function, described below
in this chapter, is enabled, the print time interval is forced to zero. Pressing SERIAL only
causes the print to occur when the measurement has stabilized (HOLD symbol still). Later, it
is possible to repeat the print at will, but while the HOLD mode is on, the sample identifier
number is not increased. This is useful when more labels must be printed with the same
identification code without increasing the code each time.
The message "SMPL ID UNT=RSET SER=PRNT" is scrolled in the comment line: using
the arrows ( and ) the currently measured sample identifier value can be changed.
By holding the °C/°F (Unit) key down the proposed number is rapidly set to zero.
The instrument's heading information will be printed using the SERIAL key.
3) AUTO-HOLD function: the instrument normally operates in continuous view mode (de-
fault setting). In this mode the displayed measurement is updated every second. If the Auto-
Hold function is enabled, the instrument performs the measurement and when it stabilizes it
goes in HOLD mode. To update the display indication, press FUNC/ENTER. The Auto-
Hold function is applied to the pH measurement, conductivity and all resulting measure-
ments.
In the following figure you can see an example of the measurement process with the Auto-
Hold function enabled. A probe is immersed into a liquid at conductivity 1 and, to perform
the measurement, the FUNC/ENTER key is pressed: The conductivity measurement raises
progressively reaching the final value. The HOLD symbol blinks. In the stretch indicated by
1, the measurement remains stable for 10 seconds, within two digits: at the end of this inter-
val (point 2), the instrument goes into HOLD mode, presenting the final stable value.

HD2156 - 12 - V2.5
2 digit
10s
t


4) Print and log interval: sets the interval in seconds between two loggings or data transfers
to the serial port. The interval can be set at 0, 1s, 5s, 10s, 15s, 30s, 60s (1min), 120s (2min),
300s (5min), 600s (10min), 900s (15min), 1200s (20min), 1800s (30min) and 3600s (1hour).
If the value 0 is set, SERIAL works on command: the sending of data to the serial port
is performed each time the key is pressed. Recording (LOG) is performed with one sec-
ond intervals even if the interval is set to 0. With an interval from 1 to 3600s, continuous da-
ta transfer is started when the SERIAL key is pressed. To end the recording (LOG) and con-
tinuous data transfer operations (SERIAL with an interval greater than 0), press the same
key again.
5) Sleep_Mode_LOG (Automatic turning off during recording) (only HD2156.2): this
function controls the instrument's automatic turning off during logging, occurring between
the capture of a sample and the next one. When the interval is lower than 60 seconds, the in-
strument will always remain on. With intervals greater than or equal to 60 seconds, it is pos-
sible to turn off the instrument between loggings: it will turn on at the moment of sampling
and will turn off immediately afterwards, thus increasing the battery life. Using the arrows
select YES and confirm using ENTER in order to enable the automatic turning off, select
NO and confirm to disable it and keep the instrument on continuously.
Note: even if Sleep_Mode_LOG=YES is selected, the instrument does not turn off for less
than one minute intervals.
6) LAST CAL pH m/d h/m (Last pH calibration): the display shows the month and day
(m/d) in the main line, and the hour and minutes (h/m) in the secondary line of the last pH
electrode calibration. This menu item cannot be modified. The calibration year is not dis-
played.
7) BUFR_1_pH (First pH buffer): selects the value of the first buffer for the pH electrode
calibration. The preset buffers are compensated for temperature. The ATC indication is dis-
played in the lower line. The USER buffer, defined by the user, is not compensated for tem-
perature: to change its value, go to the "SET USER BUFR pH" step. Please see the para-
graph dedicated to pH calibration on page 17.
8) BUFR_2_pH (Second pH buffer): selects the value of the second buffer for the pH elec-
trode calibration. No buffer solution values too close (less than 2pH) to the first buffer are
proposed. This is also true for the USER buffer, defined by the user at the "SET USER
BUFR pH" step: if, for example BUFR_1=6.860 and USER=5.000, the BUFR_2 USER
does not appear among the values because it is too close to BUFR_1. The selection NIL
(=no buffer) disables the current buffer. The USER buffer, defined by the user, is not com-
pensated for temperature. Please see the paragraph dedicated to pH calibration on page 17.
9) BUFR_3_pH (Third pH buffer): selects the value of the third buffer for the pH electrode
calibration. No buffer solution values too close (less than 2pH) to the first two buffers are

HD2156 - 13 - V2.5
proposed. This is also true for the USER buffer, defined by the user at the "SET USER
BUFR pH" step: The selection NIL (=no buffer) disables the current buffer. The USER
buffer is not compensated for temperature. Please see the paragraph dedicated to pH calibra-
tion on page 17.
10) SET USER BUFR pH (Set user pH buffer): this is a buffer whose value can be defined by
the user using the arrows; all values from 0 to 14pH are available. This buffer is not com-
pensated for temperature, so the buffer value must be set at the actual solution temperature.
As an alternative, the correct value according to temperature can be set in the calibration
phase.
11) K CELL (Conductivity cell constant): sets the conductivity probe's cell constant nominal
value. The values 0.01, 0.1, 0.7, 1.0 and 10 cm-1 (with tolerances from –30% to +50% of
nominal value) are admitted. The cell constant must be inserted before starting the probe cal-
ibration. An ERR signal is generated if the cell constant's actual value exceeds the limits –
30% or +50% of nominal value. In this case it is necessary to check that the value set is cor-
rect, that the calibration solutions are in good state, and then proceed with a new calibration.
The cell constant change entails resetting the calibration date: a new calibration updates the
calibration date.
12) LAST CAL K COND m/d h/m (Last conductivity calibration): the display shows the
month and day (m/d) in the main line, and the hour and minutes (h/m) in the secondary line
of the previous calibration of the conductivity probe. This menu item cannot be modified.
The calibration year is not displayed. The cell constant change using the K CELL_COND
parameter, resets the date.
13) ALPH_T_COND (Temperature coefficient T): the temperature coefficient T is the per-
centage measurement of the conductivity variation according to temperature and is ex-
pressed in %/°C (or %/°F). The admitted values vary from 0.00 to 4.00%/°C. Use the arrows
( and ) to set the desired coefficient T, and confirm with ENTER.
14) REF_TEMP_COND (Conductivity reference temperature): it indicates the temperature
to which the displayed conductivity value is standardized and can be equal to 20°C or 25°C.
Using the arrows ( and ), set the desired value and confirm with ENTER.
15) TDS COND (Conversion factor χ/TDS): it represents the ratio between the measured con-
ductivity value and the total quantity of dissolved solids in the solution, expressed in mg/l
(ppm) or g/l (ppt). This conversion factor depends on the nature of the salts present in the
solution: in the field of water quality treatment and control, where the main component is
CaCO3 (Calcium Carbonate), a value of 0.5 is usually used. For agriculture water, for ferti-
lizers preparation, and in hydroponics, a factor of about 0.7 is used. Using the arrows (
and ), set the desired value, selecting it in the 0.4…0.8 range, and confirm with ENTER.
16) RCD MODE (Record mode): the instrument captures a pH, a conductivity and a tempera-
ture value every second. If the RCD MODE parameter is set to "conductivity", the maxi-
mum (MAX) and minimum (MIN) values displayed using FUNC/ENTER refer to conduc-
tivity: the indicated temperature and pH are those measured at the maximum and minimum
conductivity and are not the maximum and minimum temperature and pH.
Similarly, if the RCD MODE parameter is set to "pH", the maximum and minimum values
displayed using FUNC/ENTER refer to pH: the indicated temperature and conductivity are
those measured at the maximum and minimum pH and are not the maximum and minimum
temperature and conductivity.
If the RCD MODE parameter is set to "tp" (=temperature), the maximum and minimum
values displayed using FUNC/ENTER refer to temperature: the indicated conductivity and

HD2156 - 14 - V2.5
pH are those measured at the maximum and minimum temperature and are not the maxi-
mum and minimum conductivity and/or pH.
Finally, if the RCD MODE parameter is set to "Indep" (=independent), the maximum and
minimum values displayed using FUNC/ENTER are independent: the indicated pH, conduc-
tivity and temperature are the maximum and minimum measured values but are not neces-
sarily referred to the same measurement moment (factory default).
17) Probe type: the message "PRBE_TYPE" is scrolled in the comment line. The main line in
the center of the display shows the type of temperature probe connected to the instrument.
Conductivity/temperature combined probes with Pt100 or Pt1000 sensor, or temperature on-
ly probes can be connected to the input.
4-wire Pt100 using the TP47 module
2-wire Pt1000 using the TP47 module
Upon being turned on, the instrument automatically detects the temperature probes: the
Probe Type menu item is configured by the instrument and cannot be modified by the user.
If no temperature probe or combined probe with temperature sensor is connected, the in-
strument selects the Pt1000 sensor.
18) YEAR: to set the current year. Use the arrows to modify this parameter and confirm using
ENTER.
19) MNTH (month): to set the current month. Use the arrows to modify this parameter and con-
firm using ENTER.
20) DAY: to set the current day. Use the arrows to modify this parameter and confirm using
ENTER.
21) HOUR: to set the current hour. Use the arrows to modify this parameter and confirm using
ENTER.
22) MIN: to set the current minutes. In order to correctly synchronize the minute, it is possible
to reset the seconds by pressing the °C/°F key. Use the arrows to set the current minute plus
one, and as soon as that minute is reached press °C/°F: this synchronizes the time to the
second. Press ENTER to go onto the next item.
23) BAUD_RATE: indicates the frequency used for the serial communication with the PC.
Values from 1200 to 38400 baud. Use the arrows to modify this parameter and confirm us-
ing ENTER. The communication between instrument and PC (or serial port printer)
only works if the instrument and PC baud rates are the same. If the USB connection is
used this parameter value is automatically set (please see the details on page 39).
LOG/DumpLOG key - only HD2156.2
In measurement mode, this function starts and stops the logging of a data block to be saved in the
instrument's internal memory. The data logging frequency is set in the "Print and log interval"
menu parameter. The data logged between a start and subsequent stop represent a block.
When the logging function is on, the LOG indication is displayed, the battery symbol blinks and a
beep is issued each time a logging occurs; the battery symbol does not appear when using an
external power supply.
To end the logging, press LOG.
If the Auto-HOLD function is enabled (please see the menu), the data logging is disabled.

HD2156 - 15 - V2.5
The HD2156.2 can turn off during logging between one capture and the next: the function is con-
trolled by the Sleep_Mode_LOG parameter. When the logging interval is less than one minute, the
logging instrument remains on; with an interval of at least one minute, it turns off between one cap-
ture and the next if the parameter Sleep_Mode_LOG=YES.
>>>
Dump LOG - only HD2156.2
When the LOG key is pressed after the MENU key, the transfer of the logged data on the serial port
is started.
Please see the paragraph dedicated to data transfer on page 39.
SERIAL key - only HD2156.1
SERIAL/EraseLOG key - only HD2156.2
In measurement mode, this function starts and stops the data transfer to the RS232C serial output.
According to the settings entered in the Print and log interval menu item, a single sample can be
printed if Print and log interval=0 or a continuous indefinite printing of the measured data can be
set up if Print and log interval=1…3600.
The printing operation is accompanied by the display of the RS232 symbol and the blinking of the
battery symbol; when using an external power supply the battery symbol does not appear.
Press SERIAL to end the continuous printing.
Before starting the printing with SERIAL, set the baud rate. To do so, select the Baud Rate menu
item and select the maximum value equal to 38400 baud by using the arrows. Confirm by pressing
ENTER.
The DeltaLog9 software for PC will automatically set the baud rate value during connection. If you
are using a different program than DeltaLog9, be sure the baud rate is the same for both the
instrument and the PC: the communication will only work in this way.
>>>
Erase memory - only HD2156.2
When pressed after the MENU key, the SERIAL key permanently erases all the data contained in
the instrument's memory.

HD2156 - 16 - V2.5
pH MEASUREMENT
The instruments work with pH measurement electrodes, redox potential measurement electrodes
(ORP), and specific ion electrodes. The pH measurement must always be accompanied by a tem-
perature measurement. The probes with 4-wire Pt100, 2-wire Pt1000 sensors may be used for meas-
uring temperature or for the automatic compensation of the Nernst coefficient with the pH elec-
trode.
The pH or mV indication is displayed in the main line by pressing the "pH/mV" key; the secondary
line shows the temperature. If no temperature probe with temperature sensor is connected, the sec-
ondary line shows the manual temperature.
The electrode for pH measurement
The electrode for pH measurement, generally in glass, generates an electrical signal proportional to
the pH according to Nernst law. Of this signal the following aspects are considered:
Zero point: The pH where the electrode generates a potential of 0 mV. In most electrodes, this value
is found at about 7pH.
Offset or Asymmetry Potential: mV generated by an electrode when immersed in a standard solution
at 7pH. Generally oscillates between ± 20 mV.
Slope: response of the electrode expressed in mV per pH units. The theoretical electrode slope at
25°C is 59.16 mV/pH. When the electrode is new the slope is close to the theoretical value.
Sensitivity: it is the electrode's slope expression in relative terms. It is obtained by dividing the actu-
al value of the slope by the theoretical value, and is expressed as a %. The asymmetry potential and
the slope vary in time with the use of the electrode, which necessitates regular calibration.
The pH electrodes must be calibrated using the standard solutions (see the pH calibration chapter
below). The ORP and specific ion electrodes do not need calibration as their absolute voltage is
measured. The standard redox solutions are only used to check the quality of a redox elec-
trode.
No calibration of the temperature sensor is required by the user: the 4-wire and 2-wire probes
with direct input are checked for conformity with class A tolerance according to norm IEC751 -
BS1904 - DIN43760.
The probes are detected during turn on, and this cannot be performed when the instrument is
already on, therefore if a probe is connected and the instrument is on, it is necessary to turn it
off and on.
AUTOMATIC OR MANUAL pH COMPENSATION
In a correct measurement of pH, the results need to be expressed together with the temperature val-
ue at which the reading is performed.
The electrode slope varies according to the temperature in a known mode according to Nernst law:
e.g., a 1pH variation, that at 25°C means 59.16mV, at 100°C means 74.04mV.

HD2156 - 17 - V2.5
6pH 7pH
pH
8pH
74.04mV
-74.04mV
59.16mV
-59.16mV
54.20mV
-54.20mV
0mV
mV
T=100°C, 74.04mV/pH
T=25°C, 59.16mV/pH
T=0°C, 54.20mV/pH
When a temperature probe is present, the instrument automatically applies the ATC automatic tem-
perature compensation function. To disable it, the temperature probe must be disconnected.
If the temperature probe is not present, and the correct value is not entered manually, the extent of
the error committed in pH measurement is proportional to temperature and pH value itself.
In absence of the temperature probe, the lower display shows the manually set compensation tem-
perature (default=25°C).
To point this condition out, the °C or °F symbol blinks intermittently near the temperature value.
Moreover, on the main display an "m" (manual) is turned on near the battery symbol (if present).
On the print-outs, the MT indication is printed. Instead, if the probe is present, the AT symbol is
printed.
To manually change the compensation temperature press °C/°F once: the indicated temperature val-
ue starts blinking. Select the desired temperature value by using the arrows and confirm with
ENTER. The display stops blinking, and the temperature displayed is used for compensation.
To change the unit of measurement between °C and °F, it is necessary to press twice the °C/°F key.
PH ELECTRODE CALIBRATION
The electrode calibration is used to compensate the zero potential and slope deviations to which the
electrode is subject with time.
The calibration frequency depends on the accuracy desired by the user and by the effects that the
measured sample have on the electrode. Generally, we recommend daily calibration, but it is the us-
er's responsibility from personal experience, to establish the most appropriate frequency.

HD2156 - 18 - V2.5
The calibration may be carried out using 1, 2 or 3 points. When using 1 point, the electrode offset is
corrected, with 2 points the offset and the gain is corrected; finally, in case a three points calibration
is carried out two offsets and two slopes are calculated, the second point is the one in which the
zero is performed.
The instrument has a memory of 13 buffers with relevant temperature compensation tables (ATC)
plus an "User" buffer, not compensated. The three buffers can be selected by using the
BUFR_1_pH, BUFR_2_pH, BUFR_3_pH menu items. Usually one for the acid, one for the neu-
tral, and one for the alkaline band will be selected:
@25°C
BUFR_1_pH (NEUTRAL)
6.860
6.865
7.000
7.413
7.648
BUFR_2_pH (ACID)
1.679
2.000
4.000
4.008
4.010
BUFR_3_pH (ALKALINE)
9.180
9.210
10.010
The buffers in bold are predefined in the factory, these are the "DeltaOHM" ones.
If electrode calibration was not carried out on the instrument, or the batteries have been changed
or the last calibration failed, the display blinks the CAL message.
Calibration procedure
1. Display the measurement in pH by pressing the "pH/mV" key.
2. Insert the temperature probe and the electrode in the solution of a calibration buffer. If no tem-
perature probe is available, use another thermometer and enter the value manually as indicated
in the paragraph "Automatic or manual pH compensation".
3. The electrode calibration mode is started by pressing CAL.
4. Among the three prepared buffers, the instrument automatically detects the closest to the pH
value being read and flags it up on the lower display. If the buffer is not detected the first buffer
BUFR_1_pH is proposed.
5. At this point the CAL symbol is not blinking on the display and the following is shown from
the upper side downward:
a) the chosen buffer nominal value at 25°C (scrolling indication)
b) the pH measurement value with the current calibration
c) the temperature compensated buffer value
6. The detected and temperature compensated buffer value, shown in the lower line, can be modi-
fied using the arrows.
7. To proceed with the calibration press ENTER. The electrode offset mV value (OFFS) is shown
on the display for few seconds.
8. After a few seconds the instrument shows the measurement again, corrected according to the
new calibration, but remains in calibration mode. Pressed repeatedly the ENTER key allows
the calibration on the point to be repeated, for example, in order to obtain a more stable value.
9. To end the electrode calibration, press "ESC" to exit calibration, or continue the calibration for
the second point.
10. Extract the electrode from the buffer, clean it carefully, and insert it in the following buffer.

HD2156 - 19 - V2.5
11. Press the MENU key.
12. The instrument displays the value detected on the new buffer: continue by repeating the steps
from point 4.
NOTES:
After calibration, the instrument displays an electrode quality indication:
No signal: electrode functioning.
1 small square blinking on the lower right: electrode almost exhausted.
2 small squares blinking on the lower right: electrode exhausted to be replaced.
The 3 point calibration must always be carried out according to the fixed sequence:
NEUTRAL>>ACID>>BASIC. The basic buffer must be the last in the sequence.
Without having pressed ENTER at all, the calibration is interrupted by pressing ESC; the
previous values will continue to be used.
The buffers are always presented in the sequence set in the menu with the BUFR_1-BUFR_2-
BUFR_3 parameters. The 2 point calibration is possible using the sequence BUFR_1-BUFR_2
or BUFR_2-BUFR_3 or even BUFR_1-BUFR_3. The 3 point calibration is only possible us-
ing the exactly described sequence BUFR_1-BUFR_2-BUFR_3.
Allowed pH calibration sequences
Number of cal-
ibration points
1
BUFR_1
BUFR_2
BUFR_3
2
BUFR_1 - BUFR_2
BUFR_2 - BUFR_3
BUFR_1 - BUFR_3
3
BUFR_1 - BUFR_2 - BUFR_3
A buffer can be disabled in the option selection phase (MENU mode) by choosing the NIL val-
ue. In this case, the disabled buffer is excluded from the sequence and will not be proposed.
If no other buffer is expected after the first, as the BUFR_2 and BUFR_3 have been set to NIL,
the calibration mode is exited by pressing MENU.
In any case where no operation is performed, the calibration mode automatically stops af-
ter 60 seconds.
If the calibration is rejected by the instrument because it is considered to be excessively corrupt-
ed, the CAL ERR message will appear, followed by a long beep. The instrument remains in cal-
ibration mode and maintains the previous calibration values: at this point, if the calibration is in-
terrupted using ESC, the instrument signals the anomaly through the CAL message blinking.

HD2156 - 20 - V2.5
Temperature characteristics of Delta OHM pH standard solutions
The 13 standard solutions reported in the table on page 18 are memorized in the instruments with
relevant variations according to temperature: The characteristics of the three Delta Ohm standard
buffers at 6.86pH, 4.01pH and 9.18pH (@25°C) are reported below.
6.86 pH @ 25°C 4.01 pH @ 25°C
°C
pH
°C
pH
°C
pH
°C
pH
0
6.98
50
6.83
0
4.01
50
4.06
5
6.95
55
6.83
5
4.00
55
4.07
10
6.92
60
6.84
10
4.00
60
4.09
15
6.90
65
6.85
15
4.00
65
4.10
20
6.88
70
6.85
20
4.00
70
4.13
25
6.86
75
6.86
25
4.01
75
4.14
30
6.85
80
6.86
30
4.01
80
4.16
35
6.84
85
6.87
35
4.02
85
4.18
40
6.84
90
6.88
40
4.03
90
4.20
45
6.83
95
6.89
45
4.05
95
4.23
9.18 pH @ 25°C
°C
pH
°C
pH
0
9.46
50
9.01
5
9.39
55
8.99
10
9.33
60
8.97
15
9.28
65
8.94
20
9.22
70
8.92
25
9.18
75
8.90
30
9.14
80
8.88
35
9.10
85
8.86
40
9.07
90
8.85
45
9.04
95
8.83