Frequently Asked Questions
Does Signal COM (SCOM) connect with Power Ground (COM)?
Yes, Output Ground Common (SCOM in DB-25 & COM in screw terminal blocks) is the same as Power Ground Common (COM in Main Power & Alternate Power screw terminal blocks).
This is true for 8BP01, 8BP02, 8BP04, 8BP08, and 8BP16.
KEYWORDS/PHRASES: SCOM, COM, 8BP01, 8BP02, 8BP04, 8BP08, 8BP16, common, signal common
What is the function of backpanels for signals?
Think of the backpanel as a bidirectional signal transfer device whose direction is determined by the module in a particular channel.
For an input module, the signal is transferred from the field-side screw terminals to the system/power supply-side screw terminals or to a signal access ribbon cable header or D-sub connector.
For an output module it is just the reverse, the signal is transferred from the system/power supply-side screw terminals or from a signal access ribbon cable header or D-sub connector to the field-side screw terminals.
Keywords/Phrases: backpanel, 5B backpanel, 7B backpanel, 8B backpanel, SCMD backpanel
How do I verify module accuracy?
Long story short, they believe the modules may be less accurate than specified. The biggest error seems to be a low voltage (1-2V), with error decreasing as Vin approaches 10V.
The biggest error at low voltage with error decreasing as Vin approaches 10V means that they are calculating error as % of reading.
Accuracy of Dataforth modules is specified and calculated as % of Span. The method is the following.
Set the test voltage.
Apply it to the module input.
Measure the voltage at the module input.
Calculate the expected module output voltage using the measured input voltage.
Measure the output voltage.
Calculate the % of Span error by the following formula.
Accuracy error % Span = ((Measured Vout – Calculated Vout) / Output Span V ) x 100
This method works for input or output modules.
Keywords/Phrases: Module accuracy, accuracy %, accuracy % of Span, Dataforth method for calculating Span accuracy
Can Dataforth provide calibration reports for modules I purchased?
Yes we can provide calibration reports for the modules that you purchased.
You can either
a) visit https://www.dataforth.com/TestDataReport.aspx to search for Test Report Datasheets by Serial Number or
b) you can send us a list of model numbers and their serial numbers to email@example.com
Am I right in assuming that the 8B modules cannot be Re-Calibrated in the field or by Dataforth?”
Dataforth modules are all designed to be highly stable, thus they do not require re-calibration.
8B modules cannot be re-calibrated in the field, but they can be re-calibrated by Dataforth.
We do offer a re-calibration service. For details, please contact sales by email at firstname.lastname@example.org or by phone at 1 800 444 7644 press 1 for Sales.
Analog Devices announced a last time buy and discontinuance of their signal conditioning modules. Can I replace them with Dataforth signal conditioning modules?
Yes, in general, Dataforth signal conditioning modules are a direct replacement for all Analog Devices signal conditioning modules. e.g. "SCM5B35-xx: Linearized 4-Wire RTD Input Modules" will replace Analog Devices "5B35: Isolated 4 Wire RTD Input Signal Conditioning Module".
Please note that Dataforth signal conditioning modules are RoHS II compliant.
Why do I get no output on an 8B backpanel from an 8B input module?
On the isolated field side of the 8B backpanel, use the shorter screw terminals that are offset to the right and marked “-“ and “+” for the inputs to the module. Use the taller screw terminals that are offset to the left and marked “-EXC” and “+EXC” for modules that provide excitation.
Keywords/Phrases: 8B, 8B module, 8B input module, 8B backpanel
What is the total power consumption of the 8B backpanel?
The total power requirement on the 5VDC power rail is the summation of the power requirement of the individual modules as specified in each module specification. For power budget purposes, multiply the total power requirement you calculated by 1.5 for maximum power needed.
KEYWORDS/PHRASES: 8B backpanel, power consumption, power requirement, total power, total power requirement
Is the optional plug-in conversion resistor required in order to use the 8B32 module?
No, the optional plug-in conversion resistor is not shipped with nor is it required in order to use the 8B32 module. The current/voltage conversion is achieved by an internal resistor as shown in the block diagram in the data sheet.
The optional plug-in resistor could be used to shunt off some of the current from the module and allow a larger input current range; then it could also be used with voltage input modules to convert a non-standard current range into an input voltage range.
Keywords/Phrases: 8B32, internal resistors, plug-in conversion resistor
The SCM5B42 can function as an SCM5B32, why can't the 8B42 function as an 8B32?”
The 5B42 has separate passive input connections on +In and -In and the 8B42 does not. If you notice, the - input (pin 3) on the 8B42 has NC (No Connection) to the internal circuits of the module.
The 8BB42 can only be used with passive 2-wire transmitters because the only connection into the module is through the +EXC (excitation power out) and the + (return signal current input) connection.
In the 8B product line, the customer will have to use the 8B32-01 passive current input module.
Keywords/Phrases: 5B, 5B42, 8B, 8B42, 8B32-01, passive 2-wire transmitters, passive current input
Does SCOM 0 to xx (15 max) connect to one signal common COM?
All Signal COMmon (SCOM) for all channels are connected to one signal common COM.
This is true for 8BP02, 8BP04, 8BP08, and 8BP16.
KEYWORDS/PHRASES: SCOM, COM, 8BP02, 8BP04, 8BP08, 8BP16, common, signal common, backpanel
Is the optional plug-in conversion resistor required in order to use the 8B42 module?
No, the optional plug-in conversion resistor is not shipped with nor is it required in order to use the 8B42 module. The current/voltage conversion is achieved by internal an resistor as shown in the block diagram in the data sheet.
Keywords/Phrases: 8B42, internal resistors, plug-in conversion resistor
Can the 8B41-12 withstand 300V input without damage?
The 8B41-12 module can withstand 300VDC continuous on its input terminals without damage. However, the output voltage will go to one of the internal power supply rails and remain there for several seconds after the input returns within the specified +/-60V input range."
Can you explain what is the difference between the “Standard frequency range” and the “Extended frequency range” for the 8B33 module? I don’t see an option to order different module type so how are the two frequency ranges accessible to the user ?
The user does not have to do anything special; the module operates seamlessly over the full frequency range of 45Hz to 10kHz. We needed to split the full frequency range into two ranges so we could define and specify the different accuracy levels associated with each subrange.
If you look further down the 8B33 Specifications under Accuracy, you will notice the extended frequency range carries an additional +/-1.375% Span error and +/-3.25% Span error (-06). This error is in addition to the +/-0.25% Span error at 50/60Hz. So the total accuracy error will be +/-0.25% + (+/-1.375%) = +/-1.625% Span and . +/-0.25% + (+/-3.25%) = +/-3.50% Span.
Keywords/Phrases: 8B RMS, 8B True RMS, 8B RMS input module, 8B True RMS input module, 8B33
I have an 8B33 module, what is the accuracy error between 0-5% span?
In the 8B33 data sheet, Note 4, For 0-5% Span measurements add 1% accuracy error (-02, -03, -04, -05) or 1.5% accuracy error (-01, -06). Accuracy error includes linearity, hysteresis and repeatability but not source or external shunt inaccuracy (if used).
Keywords/Phrases: 8B RMS, 8B True RMS, 8B RMS input module, 8B True RMS input module, 8B33 accuracy, span, offset
Can I power multiple 8B backplanes off of a single power supply?
You can use a single 5V power supply to power multiple backplanes, but you need to be aware of the current rating of your power supply and the current draw of your 8B modules. The current rating of your power supply needs to be greater than the total current draw of all the modules in your system (ideally 1.5x the total current draw). You can check the current draw of various 8B modules by checking their datasheets.
What is the output resistance, how does the filtering work and what are the overshoot characteristics for a 8B51-03?
The 8B51-03 has an output resistance < 1 Ohm.
Its filter is a five-pole low pass filter which attenuates gradually up to the -3dB frequency of 20kHz above which it attenuates sharply at 100dB per decade of frequency. The filter has no overshoot because it is critically damped.
What does “sensitivity” mean on my strain gage input module?
The sensitivity is listed on the datasheet to help determine what strain gages/load cells will be compatible with that module. Strain gages do not have a specific voltage output range (i.e. -30mV to 30mV) but rather a voltage output range that varies depending on the excitation voltage applied to the strain gage (its "sensitivity"). Since our strain gage modules have a fixed voltage input range and a fixed excitation voltage, the sensitivity is the most reliable way to determine if a strain gage is compatible with our module.
For example, a load cell with a 3mV/V sensitivity will output 30mV at full scale with a 10V excitation voltage, because 3mV/V * 10 V = 30mV. A signal conditioner with a 10V excitation and a -30mV to 30mV input range will be compatible with a load cell of 3mV/V sensitivity.
Why do Dataforth’s linearized thermocouple modules have a low bandwidth of 3-4 Hz?
Our linearized thermocouple modules have a bandwidth of 3-4 Hz in order to reject any induced noise along the sensor line. If a wider bandwidth is needed, a custom module could be designed and manufactured to meet the required specifications. Contact Dataforth at email@example.com to discuss your specific needs.
8B backpanels: Are these products ESD sensitive? And if so, should the product be in sealed static shielding bags, and not an “Antistatic” bubble wrap, when shipped?
Static shielding bags are not necessary since the 8B backpanels are not ESD sensitive. The risk of physical damage is greater than the risk of ESD damage.
Keywords/Phrases: 8B backpanel, 8B backpanel ESD sensitivity, ESD, ESD sensitivity
On the 8B51, can I apply the + and – input leads “backwards” to reverse the polarity of the output signal?
This can be done only if the voltage source is floating (isolated); this pertains also to the SCM7B modules.
Better modules for true differential operation for which a floating source is not needed are the DSCA30/31/40/41. Other modules for this type of operation are the SCM5B30/31/40/41 used with an SCMPB07-x with the I/O COM jumpers Jn removed in the channels for which true differential operation is desired. Both the DSCA and the SCM5B outputs can float +/-50V with respect to power supply common.
Keywords/Phrases: 8B51, reverse input leads, true differential
Does Dataforth have any options for thermistor input?
Thermistor interface has never been designed for SCM7B, 8B, DSCT, or MAQ20 product lines. However, we do have some custom products in the SCM5B line that can accept thermistor interface. Any SCM5B36, SCM7B36, 8B36, DSCA36, DSCT36 module with potentiometer input 0-10kohm may also be suitable for some sensors.
Why do only a few 8B modules have a +/-5V output?
Some 8B modules (such as 8B34 and 8B47) cannot have bipolar output due to limitations in the internal linearization circuitry.
If I were to put a 120 ohm bridge onto an 8B38-02 (range of 300 ohm to 2K ohm), what happens to the supply voltage and will the system work?
If you were to put a 120ohm bridge into an 8B38-02 the excitation voltage won’t regulate, and it won’t provide the proper amount of excitation. The load range must be in the specified range.
If I purchase a backplane with no CJC, will I still be able to use modules that require the CJC enable jumper to be installed?
Yes. Backplanes with no CJC will still come with the CJC enable installed on the backplane.
If I don’t have an 8BPWR-2, can I use a +5VDC power supply to power my 8B backplane?
Yes, you can. The 8BPWR-2 is not required to power the 8B backplanes, it is used in situations where you don't have a +5VDC power supply and need to regulate the voltage of whatever current power supply you are using down to +5VDC so that it can be used for the 8B backplane.
Please make sure when choosing your +5VDC power supply that the current rating of the supply is acceptable for the total current draw of your system.
Is there an 8B module which can accept up to +/-50V, has >10k input resistance, <100 Ohm output resistance and can be sampled up to 250kHz?
The 8B51-12 can accept up to +/-60V input.
It has >500k Ohms input and <1 Ohm output resistance.
It could be sampled at 250kHz, but it will present unchanging data within +/-0.08% up to 92% of the samples. For it to provide new data it can be sampled up to a 20kHz sample rate.
What is the recommended power supply for Dataforth SCM5B and 8B modules?
The recommended power supply for the Dataforth SCM5B and 8B modules are the linear power supplies in our SCMXPRT/SCMXPRE series. The SCMXPRT/SCMXPRE power supplies output 5V and have options for 1A output current (SCMXPRT-001) or 3A output current (SCMXPRT-003).
The SCMXPRE series is identical to its SCMXPRT counterpart, but is configured for European voltage standards.
The SCMXPRT-001/SCMXPRE-001 both have the option for DIN rail mounting as well (SCMXPRT-001D/SCMXPRE-001D).
Other power supplies that meet that power requirements of the SCM5B and 8B modules can be used as well, but it is strongly recommended to use a linear power supply rather than a switch-mode power supply. Switching power supplies can add noise artifacts to the output of your modules.
How do I convert an RMS voltage to its corresponding peak voltage?
To convert an RMS voltage to its corresponding peak voltage, you simply take the RMS voltage value and multiply it by the square root of 2, or roughly 1.414.
For example, 1500Vrms corresponds to a peak voltage of 1500 * 1.414 = 2121 Vp
Is the calibration of Dataforth modules traceable to NIST standards?
Yes, calibration of Dataforth modules is traceable to NIST standards.
For 8B49 modules when I give LabVIEW (or other DAQ software) an output command, I get no output from the backpanel, why?
That’s because the 8B49 and the 8B39 are output modules, are connected the reverse of input modules, they have their inputs on the system side (power supply side) of the backpanel. They provide their output on the isolated field side of the backpanel.
Keywords/Phrases: 8B, 8B module, 8B output module, 8B49, 8B39
Does Dataforth carry any signal conditioners that interface with AC LVDTs?
Although we do not carry signal conditioners that can interface with AC LVDTs, we do have the SCM5B43, 8B43 and DSCA43 which can interface with DC LVDTs.
If someone accidentally connected a powered sensor (0-5V analog signal) to the input of an 8B38 would it damage it?
The 8B38 has an input protection of 240VAC continuous, so a 0-5V input will not damage the device. You can apply a continuous signal of up to 240VAC before the input will start to get damaged.
How does the load resistance of a module affect the noise at the output?
Noise at the output of a module is independent of load resistance.
If the input range of my signal conditioner is -1V to +1V and the output range is 0 to 10V, does this mean that it ignores polarity?
A signal conditioner with these I/O ranges does not mean that the module ignores the polarity of your voltage input. The output of voltage input modules are scaled linearly, meaning an input of -1V would correspond to an output of 0V, an input of 0V would correspond to an output of 5V, an input of +1V would correspond to an output of 10V, and so on.
Does Dataforth have an SLX300 system with more than 4 Analog output channels?
No, the microcontroller used for analog I/O on the SLX300 can only support 4 channels of analog output.
Is the SCMXPRT-003 DIN rail mountable?
The SCMXPRT-001 has an option for DIN rail mounting (part number: SCMXPRT-001D) but the SCMXPRT-003 does not. Instead, it can be mounted on the SCMXRK-002 which is a 19 inch metal rack for mounting the SCMXPRT-003 as well as various Dataforth backpanels and the SCMXIF interface board.
What is the correct backpanel for my 8B38 module?
Any of the backpanels in the 8B series will work for the 8B38 module. In fact, any of the 8B modules can be mounted to any of the 8B backpanels.
If a thermocouple is soldered to a lead that has current running through it, how do you avoid affecting the thermocouple signal and subsequent measurement?
The thermocouples must be isolated so current does not come from the circuit under test and run through them. SCM5B, SCM7B, 8B, DSCA, DSCT, MAQ20 all offer the required isolation.
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