Adding a Site Offset to SDI12 Output
In some applications it is necessary to measure a site value including some
reference data point, for example sea level. Assuming the sensor is installed 10m
above sea level, then it is possible to have all reported readings add 10m, thus
acquiring the data without the need for further modification. To add a site offset
then:
1. Determine the offset to be applied.
2. Add the offset to the pressure units (e.g. aXU1,10!)
3. Save new calibration to nonvolatile memory (e.g. aXS0!)
4. Verify sensor now measures 10m for 0 applied pressure.
10. WARRANTY
The company warrants its products to be free from defects in material and
workmanship in normal use and service for a period of two years from date of
shipment. The Company reserves the right and option to repair or replaceupon
evaluation of the returned original part. Modification, misuse, attempted repair by
others, improper installation or operation shall render this guarantee null and
void. The Company makes no warranty of merchantability or fitness for a part or
purpose.
11. Servicing
The transducer cannot be repaired locally and if damaged should be returned to
ourselves at the address shown below when a replacement/repair is required.
Setra Systems, Inc.
159 Swanson Road
Boxborough, MA 01719
Attn: Repair Department
Model 595 Slimline
Submersible Pressure Transducer
12. Return to Factory
PLEASE NOTE: All returns must be accompanied with Setra’s “Calibration and
Service Order” return form. The form can be downloaded at:
http://www.setra.com/tra/repairs/pdf/webrepair.pdf
Any instrument returned without Setra’s authorized form completely filled out
will be quarantined and no action will occur. It may ultimately be returned to you
and subject to a transportation charge.
159 Swanson Road, Boxborough, MA 01719/
Toll Free: 800-257-3872/ Phone: 978-263-1400/
Fax: 978-264-0292/Email: sales@setra.com/Web: www.setra.com
ISO
9001:
2000
Certified
✓
Setra Systems, Inc.
Contents
1.0 Introduction ........................................................................................................................... 3
2.0 Safety Instructions ................................................................................................................. 3
3.0 Hazardous Products ............................................................................................................... 3
4.0 GENERAL ................................................................................................................................ 3
5.0 Action on Receipt ................................................................................................................... 4
To re-range the 595 sensor proceed as follows:
1. Determine the 595 sensor full scale and the user application full scale.
2. Find the required calibration gain. Divide the 595 sensor full scale by the user
application full scale (e.g. 10/4)
3. Program the calibration gain into the sensor (via SDI12 interface).
(e.g. aXG2,2.5!)
4. Check the residual error with zero pressure applied. Note as the gain is increased any offset errors ban be magnified. So for example instead of 4mA
expected sensor reads 3.959mA.
5. Program offset in calibration of sensor to remove offset errors (e.g. aXA2,0.041!)
6. Save new calibration to nonvolatile memory (e.g. aXS0!)
7 Verify sensor now measures 4 to 20mA for required application range.
6.0 Installation ............................................................................................................................ 4
6.1 Lowering the Pressure Probe ......................................................................................... 4
6.2 Electrical Installation .....................................................................................................5
7.0 Operation ............................................................................................................................... 6
7.1 Analogue Output Probes ............................................................................................... 6
7.2 SDI12 Operation ............................................................................................................ 6
8. Maintenance ............................................................................................................................ 9
8.1 Self diagnostics ............................................................................................................. 9
8.2 Calibration Adjustment ............................................................................................... 10
8.3 Cleaning ...................................................................................................................... 14
9. Advanced Operation ............................................................................................................... 14
10. WARRANTY ......................................................................................................................... 16
11. Servicing ............................................................................................................................ 16
12. Return to Factory ................................................................................................................ 16
Configure a Reverse Output 20mA to 4mA.
If your application demands a 20mA output with zero applied pressure and 4mA
output for full scale applied pressure then the sensor output can be reversed by
sending the following SDI12 commands:
1. Set calibration gain of mA output to -1 (e.g. aXG2,-1!)
2. Set calibration offset of mA output to +24 (e.g. aXZ2,24!)
3. Save new calibration to nonvolatile memory (e.g. aXS0!)
4. Verify sensor now measures 20mA to 4mA for 0 to full scale applied
pressure.
Applying a Filter to the mA Output
In applications that are inherently difficult to measure, for example waves on
reservoir, then the 595 can be configured to apply a mean or median filter via the
SDI12 interface before updating the analogue mA output. The filter command is
described below:
SDI12 Command: 0XFt,nn,xxxx!
Neptune Response: 0t,nn,xxxx<CR><LF>
Where:
T = type of filter
0 = MEAN
1 = MEDIAN
nn = number of values to filter, maximum 12
xxxx = 220ms intervals between measurements, maximum period 1
hour
To apply a filter:
1. Determine the type of filter and period suitable for the application.
2. Send the filter command to the 595 sensor (e.g. 12 reading mean, sampling
period 15 minutes, aXFt,12,4091A)
3. Save the filter to nonvolatile memory (e.g. aXS0!)
4. Verify the filter performance in applications.
8.3 Cleaning
Inspection and cleaning of the product is recommended as part of a
preventative maintenance procedure. The required inspection period will depend
on the nature of the application environment. To inspect the product unscrew
the nose cover. Figure 2, and view the sensor diaphragm. The housing should be
free from deposits. Cleaning with a cotton bud (Q-TIP) is possible, but extreme
care must be taken not to deform the sensor diaphragm during cleaning.
Figure 2
Inspecting and Cleaning the Sensor
9. Advanced Operation
The 595 allows for a number of advanced operations not normally
available.
Re-Range 4 to 20mA Output
Often users wish to measure a specific water level that is not the same as the full
range output of the transducer. For example, if the sensor output was 10MH2O
and the user wishes to measure up to 4mH2O then without a down range feature
the output for the 10mH2O unit in the users applications would be 0 to 40% of
the range or 4 to 10.4mA. In this situation it is possible to use the SDI12 interface
to program calibration coefficients into the sensor to provide 4 to 20 mA for the 0
to 4mH2O application, with the 10mH2O sensor.
1.0 Introduction
Model 595 is a level measuring transducer for precise measurements of ground
and surface water levels. The transducer measures pressure and temperature
signals and, by compensating these measured values for temperature effects, the
relative density of water and the specific gravity in the users location, provide a
highly accurate and repeatable “true” level measurement. The resultant level is
available either as an analogue output or as a digital output
2.0 Safety Instructions
Important Note: Setra’s Model 595 pressure transducer is designed and manufactured in accordance with Sound Engineering Practice as defined by the Pressure
Equipment Directive 97/23/EC. Pressure transducer products designed to meet
the highest risk category “IV” of the Pressure Equipment directive are clearly
marked on the label by “CE0086”. Compliance is achieved through modules “B&D”.
No other products should be used as “Safety Accessories” as defined by the PED,
Article 1, Paragraph 2.1.3.
EMC: Model 595 conforms with the essential protection requirements of the EMC
Directive 89/336/EEC amended by certified type testing to EN 61000-6-3 and
EN61000-6-2. Conformity with the requirements of the CE mark only applies
when the installation conditions described in these instructions have been met.
3.0 Hazardous Products
The 595 may be classified as Electrical, Electro-Mechanical and Electronic equipment.
These products are tested and supplied in accordance with our published
specifications or individual special requirements that are agreed in writing at time
of order. They are constructed so as not to affect adversely the safety of persons
and property when properly installed, maintained and used by qualified personnel, in the applications for which they were designed and manufactured. Refer to
installation and maintenance instructions for further details.
4.0 GENERAL
● Transducer should not be subjected to greater than maximum allowable
pressure range as defined on the transducer label.
● Transducer should not be subjected to mechanical impact.
● The effects of decomposition of unstable fluids should be considered by the
user when placing this device in service.
● Pressure range must be compatible with the maximum level being measured.
● Pressure media must be compatible with the transducer wetted parts which
are:
UNS31803 Stainless Steel, BS En 10088-3:1995 No. 1.4462.
Polyurethane
Acetal
Nitrile
● Exposed end of cable must be kept free from moisture
● Liquid must not be allowed to freeze in the pressure port.
5.0 Action on Receipt
● Check accessories supplied include Calibration Certificate
● Check details on Calibration Certificate agree with data etched on transducer.
6.0 Installation
The 595 can be put to use in various applications, for example, in tubes or
boreholes wider than one inch in diameter, in wells, open waters, and in non
permanent water carrying riverbeds. The optional sink weight prevents the probe
body from floating to the surface. The pressure probe can be easily fixated in
flowing waters or waters with waves. When designing the measurement location,
observe the hydrodynamic influence of strong currents (>0.5-1 m/s). Depending
on the version and the type of mounting of the individual components, under
pressure or over pressure may occur which may distort the measuring result.
Important: It is not recommended to install the pressure probe in the vicinity of
docks, industrial waste water discharges or areas with high chemical pollution.
The pressure probe is made of high-quality stainless steel and synthetic material.
Nevertheless damaging corrosion may occur, depending on the installation
location. For further information refer to the technical data of the wetted part
materials.
6.1 Lowering the Pressure Probe
6.1.1 First determine the minimum and maximum water levels at the measur-
ing point, for example, with a stuff gauge or contact gauge. Determine
the probe position from these two values. The following prerequisites
must be met:
* Position the probe below the minimal water level
* Difference between maximum water level and probe position <
measuring range of the probe.
6.1.2 Lower the pressure probe at the probe cable to the determined depth.
Recommended Calibration Procedure
1. Check mA Output Calibration
Acceptable?
Y
2. Check Pressure
Measurement Calibration
Acceptable?
Y
3. Check Temperature
Measurement Calibration
Acceptable?
Figure 1
Note: mA output calibration not
necessary for SDI12 operation
Calculate and set
required gain and
N
N
Note: Temperature calibration
not necessary for mA output
operation
N
slope value
Calculate and set
required gain and
slope value
Calculate and set
required gain and
slope value
6.1.3 The cable should be suspended via a suitable cable suspension acces-
sory. The integral Kevlar core provides mechanical strength within the
cable, sufficient to suspend the probe.
6.1.4 Fine adjustment of the probe position may be performed via the probes
digital interface. If the measured value is to be referenced to a zero level,
this can be achieved by adding a user offset. Therefore, in most cases a
coarse positioning of the probe is sufficient. In non permanently watercarrying riverbeds the pressure probe delivers a zero reading in a dry
condition.
Y
4. Set Calibration Dates
5. Save Calibration Data
Step 6: Apply Full Scale Value
Set Point Value 20 mA, actual reading 19.999 mA
Step 7: Calculate Errors and Record Results
Applied Measured Error
4.000 4.001 0.001
20.000 19.999 -0.001
Step 8 Write the Calibration Dates
Calibration dates are stored as nine character ASCII string. Assuming the
calibration date was March 3rd 2005, then the dates could be written as
shown in Table 14.
6.2 Electrical Installation
The 595 requires a D.C. power supply between 8V and 30V. The 595 includes
suppression devices providing surge protection. In the event of a surge these
devices can clamp across the power supply, providing protection against the
surge. To avoid damage to the protection devices the power supply must be
current limited so that the maximum normal operating current is 100mA. Where
batteries are used directly this can easily be achieved via a series resistor, of
suitable nominal value and power rating. For mA output units, the second
consideration is the total resistance in the current loop. The maximum loop
resistance is calculated by the formula:
Maximum Loop Resistance = (Vx - 8) * 50 ohms
Table 1 states the minimum and maximum resistance recommended.
Table 1
Recommended Power Supply Current Limit
Table 14
Writing the Calibration Dates
Command Response Comment
aXL,03MAR2005! a03MAR2005<CR><LF> Writes the last calibration date.
aXN,03MAR2006! a03MAR2006<CR><LF> Writes the next calibration date.
Step 9 Save the Calibration
All data written remains nonvolatile until the save command is executed
as shown in Table 15.
Command Response Comment
AXS0! a0! Saves all data
Power Supply Current Limit Series Resistance Maximum Loop
Voltage Limit Note 1 Resistance
12 0.1A 120 ohm 200 ohm
24 0.1A 240 ohm 800 ohm
30 0.1A 300 ohm 1100 ohm
Note 1.: Minimum series resistance only required where current limit of 0.1A is not
provided by power supply.
The cable comprises 4 color-coded cores, with a central vent tube, enclosed by an
aluminum/polyester screen where the screen is in intimate contact with a
separate drain wire. The outer sheath can be of various material, depending upon
application and operating temperature, standard suitable for most water environments is Polyurethane (immersed operating temperature -20°C to +50°C). Other
cables are available on request for operation at higher temperatures or in more
corrosive media. The cable should be terminated in a dry environment to avoid
moisture entering the vent tube. If water enters this tube then erroneous
measurements may result. In humid environments then it is recommended to
terminate the cable into a suitable desiccator (see Setra’s Model 299). The
following electrical connections should be made:
Table 2
Connections mA Output Probes
Wire Color Signal Name Description
Red VEx_+ve Positive Excitation for the Probe
Blue Vex_-ve Negative Excitation for the Probe
None/Screen Ground Metalwork of Probe
Green* SDI12 SDI12 Data
* Not required for 4 to 20 mA output operation
It is recommended to firmly secure the Kevlar core of the cable, for example, by
knotting and securing under a fixing screw.
7.0 Operation
Having installed the transducer as instructed it is ready for use. Before applying
power, check that the correct polarity and excitation levels are being applied. See
Electrical Installation (6.2).
7.1 Analogue Output Probes
Analogue output devices will simply provide a 4 mA output for 0 level and a 20
mA output for the full scale level indicated on the product label. The analogue
output can be adjusted via the digital SDI12 interface with a suitable accessory to
include site offsets or provide full scale, 20 mA, output at a different level.
7.2 SDI12 Operation
The SDI12 interface conforms with the SDI12 V1.3 specification. Refer to the SDI12
host web-site for a full specification, http://www.sdi-12.org.
In addition to the standard SDI12 command set, the 595 supports a number of
extended commands, providing increased levels of functionality. All sample
commands provided are shown with address “a” , to use the command substitute
the actual address of the unit. The default address when manufactured is “0”.
7.2.1 Setting up the Measured Variable
The transducer can provide either an output proportional to the applied pressure
or a true level compensated for relative density of water. The preferred measured
value must be set by the XP command as detailed in Table 3.
Table 3
Setting the Measured Variable
Command Response Comment
aXP0! a0<CR><LF> Set true level measure, compen-
sated for relative density of water
over temperature and local gravity.
aXP1! a1<CR><LF> Set pressure measure, no additional
compensation.
7.2.2 Making a Level Measurement
The corrected level measurement is calculated in the following manner.
Level = mH2O pressure at 4°C * 1 * 9.80665
density of water local gravity
where:
Density of water = -6.017777e-6t2 = 0.0000408t+0.999841
where t - temperature in °C.
Table 12
Calibration of the mA Output
Command Response Comment
aXM4 a4.00000<CR><LF> Sets the mA output to 4 mA.
Measure the current and record the actual
value.
aXM20 a20.0000<CR><LF> Sets the mA output to 20.0 mA.
Measure the current and record the actual
value.
Step 1: Apply Zero Scale Value
Set Point Value 4mA, actual reading 4.005 mA.
Step 2: Apply Full Scale Value
Set Point Value 20mA, actual reading 19.995 mA.
Step 3: Calculate the Errors and Adjustment Values
The value to write to the offset calibration adjustment is calculated by subtracting the measured value of 4mA from the 4mA
set point as shown:
Set point zero = 4.000
Measured zero = 4.005
Offset Value = 4.000-4.005 = -0.005 mA
Step 4: Write the Calibration Adjustment Values
The value to write to the gain calibration adjustment is calculated
by dividing the set point span by the measure span as shown:
Set point span = (20-4) = 16 mA
Measured span = (19.995-4.005) = 15.99 mA
Gain value = 16/15.99 = 1.0006254
Table 13 shows the command required to write the calibration adjustment to
the 595:
Table 13
Writing the mA Output Calibration
Command Response Comment
AXZ3,-0.005! a-0.00500<CR><LF> Writes the offset of -5µA to the mA
output zero.
AXG3,1.0006254! A1.006254<CR><LF> Writes the gain value t the mA
output.
Step 5: Apply Zero Scale Value
Set Point Value 4mA, actual reading 4.001mA.
8.2 Calibration Adjustment
The 595 is designed to provide excellent long-term stability, however, occasionally it is necessary to verify the calibration and perform adjustment. Setra offers an
annual recalibration service, via return to the service department. Alternatively a
two point calibration adjustment of each variable provided by the 595 is possible
via the SDI12 interface. This is achieved through three independent adjustments
i.e. pressure, temperature and mA output. The recommended calibration procedure is detailed in Figure 1. Writing of calibration adjustment values is performed
via the aXZ and aXG commands. These commands have the following syntax:
The temperature is a measured value and thus the density of water at any given
time is calculated by the transducer. The user may enter a local gravity value via
the XE command as detailed in Table 4
Table 4
Entering the Local Gravity
Command Response Comment
aXE9.81! a9.81<CR><LF> Sets the local gravity value to 9.81 m/s
2
aXZn,<value>
aXGn,<value>
where: n = channel to be calibrated
<value> = value of calibration coefficient
Three calibration channels are supported:
n = 0 = Pressure
n = 1 = Temperature
n = 2 = mA Output (response to pressure signal)
n = 3 = mA Output (fixed output)
Calibration of any channel is basically the same and consists of 9 simple steps:
1. Apply zero scale value and record the measured value.
2. Apply full scale value and record the measured value.
3. Calculate the errors and adjustment values (if required.)
4. Write the calibration adjustment values to the 595.
5. Apply zero scale values and record the measured value.
6 Apply full scale value and record the measured value.
7. Calculate new errors and record results.
8. Write the last and next calibration dates.
9. Save the calibration.
8.2.1 Example of mA Output Calibration
The mA Output consists of two discrete components:
1. The analogue to digital conversion of the measured pressure and temperature
values.
2. The digital to analogue conversion, providing the analogue output.
Step 1 in Figure 1 refers to checking the calibration of the digital to analogue
conversion of the mA output. For SDI12 output, this step is not necessary. The
calibration of mA output stage can be verified using an extended command to
set a fixed mA output value as shown in Table 12
7.2.3 Selecting a Commonly Used Unit of Measurement
For SDI12 output units it is possible to change the units of the measured variables, pressure and temperature. The extended commands aXUTn! and aXUPn!
are used to change the temperature and pressure units respectively. Note the
value of n specifies the required unit as shown in Tables 5 and 6.
Table 5
Selecting Temperature Units
Command Response Comment
aXUT0! a0<CR><LF> Sets the temperature units to °C
aXUT1! a1<CR><LF> Sets the temperature units to °F
aXUT! a1<CR><LR> Queries the temperature unit without
setting a value
Table 6
Selecting Pressure Units
Command Response Comment
aXUP0! a0<CR><LF> Sets the pressure units to mH2O
aXUP1! a1<CR><LF> Sets the pressure units to ftH2O
aXUP2! a2<CR><LF> Sets the pressure units to inH2O
aXUP3! a3<CR><LF> Sets the pressure units to bar
aXUP4! a4<CR><LF> Sets the pressure units to psi
aXUP! a4<CR><LF> Queries the pressure unit without setting a value
Note: The pressure units (bar, psi) are not valid when configured for a true level output
7.2.4 Setting Up a Custom Unit Scaling
Unit conversion performed by the 595 is of the form y=mx+c. Where units other
than the commonly used set provided are required then the m and c can be
written directly. This is achieved via the command aXUn, <value>!. Note n
represents the variable to be written with the following value as detailed in
Table 7.
Table 7
Variables Used for Unit Conversions
Value of n Variable Written
0 Pressure Units Slope = m
` 1 Pressure Units Offset = c
2 Temperature Units Slope = m
3 Temperature Units Offset = c
The value of m should be calculated as follows:
7.2.5 Obtaining Maximum and Minimum Measurements
The 595 supports the following additional measurements via the measure and
concurrent measurement commands.
aM1! = Maximum Level / Pressure
aM2! = Minimum level / Pressure
aM3! = Maximum Temperature
aM4! = Minimum Temperature
The maximum and minimum values should be reset using the XMM command
as shown in Table 10.
Table 10
Resetting Maximums and Minimums
Command Response Comment
aXMM1! a1! Resets the maximum level to the current value
aXMM2! a2! Resets the minimum level to the current value
aXMM3! a3! Resets the maximum temperature to the current value
aXMM4! a4! Resets the minimum temperature to the current value
For Pressure: m = (Full Scale in User Units – Zero Scale in User Units)
(Full scale in mH2O at 4°C – Zero Scale in mH2O at 4°C)
For Temperature: m = (Full Scale in User Units - Zero Scale in User Units)
(Full Scale in °C – Zero Scale in °C)
The appropriate values can then be written as show in Tables 8 and 9.
Table 8
Setting the Pressure Units to mbar
Command Response Comment
aXU0,98.0665! a0<CR><LF> Sets the slope m to 98.0665, equivalent to mbar.
aXU1,0! a1<CR><LF> Sets the offset to 0 as 0 mbar = 0mH2O at 4°C
Table 9
Setting Temperature Units to Kelvin
Command Response Comment
aXU2,1! a1<CR><LF> Sets the slope m as same as °C
aXU3,-273! a1<CR><LF> Sets the offset to -273 to read in Kelvin
8. Maintenance
8.1 Self diagnostics
The 595 performs a significant amount of self-diagnostics upon reception of the
verify command, aV!. It is recommended that any system design should include a
periodic execution of the verify command. The response to a verification command includes an error code. Table 11 summarizes the possible error codes from
the verification command.
Table 11
Diagnostics
Error Code Description
0 No Error, unit is functioning normally
1 The temperature measurement is beyond the calibrated range
2 The pressure measurement is beyond the calibrated range
4 The nonvolatile memory has been incorrectly accessed
8 An analogue signal error exists
16 Reserved
32 The nonvolatile user data is in error
64 The nonvolatile calibration data is in error
128 RAM error
256 Watchdog error
Note: If an error code >3 is returned, record the value and contact the manufacturer
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