DBK55

8-Channel Frequency-To-Voltage Input Module
Overview …… 2
Features of the DBK55 …… 2
Input Signal Conditioning …… 3
Edge Selection …… 4
Debouncing …… 4
Frequency Measurement …… 5
D/A Conversion …… 6

Hardware Setup …… 6
Configuring the DBK55 Module …… 6
Configuring the Primary Data Acquisition Device …… 10
CE Compliance …… 10
Connecting the DBK55 to Signals and to the Primary Data Acquisition Device …… 11

Software Setup …… 11
Specifications…… 12

Reference Notes:
o Chapter 2 includes pinouts for P1, P2, P3, and P4. Refer to pinouts applicable to yoursystem, as needed.
o In regard to calculating system power requirements, refer to DBK Basics located near
the front of this manual.

DBK55 Module

DBK Option Cards and Modules

987693

DBK55, pg. 1

Overview
Features of the DBK55
The DBK55 can be used for diverse frequency-monitoring applications. Typical uses include measuring
the flow of liquids with a flowmeter and measuring rotation (rpm) with a shaft encoder. The monitored
process must generate a series of electrical pulses whose frequency is related to the desired variable.
Features of the DBK55 include:• Inputs can be analog (high or low level) or digital.
• Each channel has a programmable frequency range.
• Noise effects can be minimized by debounce, attenuation, and low-pass filtering.
• Up to 32 DBK55s can be used with a single LogBook or Daq device for a maximum of 256
channels.
The digital-to-analog converter (DAC) outputs a voltage from -5 V to +5 V to correspond with the selected
frequency range. The DaqBook directs the DBK55 module’s DAC to convert the data from the proper
input channel.

DBK55 Block Diagram
As indicated in the next figure, the DBK55 module completes the following functions for each channel:• Conditions an input signal• Selects the signal’s rising or falling edge
• Debounces the edge
• Measures the signal’s frequency.
• Sends a voltage (Vout) analog signal [which corresponds to the measured frequency] from the DAC
to the primary data acquisition device.

These functions are discussed in the upcoming text.

DBK55 System Functionality

DBK55, pg. 2987693

DBK Option Cards and Modules

Input Signal Conditioning
The DBK55 conditions the input signal in several ways to provide the best output accuracy. Reducing
noise and limiting the bandwidth are the first steps in the conditioning process and are done in hardware.
Software can further clean up the signal by selecting the cleanest edge to read and by setting a debounce
delay to ignore spurious signals. The debounce concept is discussed on page 4.
Analog Input Signal Conditioning

WARNING
Input voltages should be at least 50 mV peak-to-peak. The maximum analog input
signal is 30 Vrms (42 Vpeak, 84 Vp-p). Stronger signals may damage the DBK55 orpresent an electrical shock hazard.

When a channel’s two “input circuit jumpers” are set for analog, the center conductor of the BNC
connector is AC-coupled through a 0.33 µF capacitor to the attenuator. The outside conductor connects toground. With the attenuator disabled [full sensitivity] input-protection diodes limit the signal to about 1.5
Vp-p. Larger signals will see an impedance of 6.7 KΩ (rather than 20 KΩ) in series with 0.33 µF. With
the attenuator enabled, the input impedance remains 20 KΩ regardless of the input level.
After AC-coupling, attenuation and filtering, a comparator converts the input signal into a clean digital
signal. The comparator output is high when the center-pin signal is higher than the outside-conductor
signal and low when the center-pin is lower than the outside-conductor signal. The comparator has
hysteresis to reduce the effects of noise by ignoring small signals.
The following graph shows typical sine-wave sensitivity in peak-to-peak voltage vs frequency. Six
combinations of attenuation (on/off) and low-pass filtering (30 Hz, 300 Hz, and 100 kHz) are graphed.

Digital Input Signal Conditioning

DBK Option Cards and Modules

987693

DBK55, pg. 3

CAUTION
The input signal may range from -15 to +15 V. Higher voltages may damage the
DBK55.
The digital input circuit is represented in the left-hand figure, below. When both of a channel’s “input
circuit jumpers” are set for digital, the outside (shield) conductor of the BNC connector connects toground. The center conductor is pulled up with 27 KΩ to +5 V and then passes through a 2.7 KΩ
protection resistor before being detected by a Schmitt-trigger buffer with input-protection diodes.
The input thresholds are fixed TTL levels. Below 0.5 V (0.8 V typical), the Schmitt-trigger buffer output
is low. Above 2.1 V (1.6 V typical), the buffer output is high. The 27 KΩ pull-up resistor allows thedigital inputs to sense switches or relays connected directly to the DBK55 as shown in the figure. The
debounce circuit can remove noise effects of switching. Debouncing is discussed later on this page.

The input impedance for digital signals depends on the signal level. For signals between 0 and 5 V, theinput-protection diodes do not conduct, and the digital input impedance is just the 27 KΩ pull-up
resistance. For signals less than 0 V or greater than 5 V, the input-protection diodes conduct and theimpedance drops to about 2.4 KΩ. The figure (upper right) shows the approximate digital-input
current/voltage relationship.

Edge Selection
The DBK55 determines the frequency by measuring the time between successive rising or falling edges of
the input signal. Which edge is electrically cleaner depends on the application and related components. If
rising edges are used, the edge-selection circuit does not modify the signal. If falling edges are used, thecircuit inverts the signal so falling edges appear as rising edges to the subsequent circuits. Throughsoftware, each channel can be independently set for rising- or falling-edge.

Debouncing
Debouncing is a process of ignoring signals too short to be real events. When a relay or switch closes, theelectrical contacts may not initially make good contact. Mechanical vibrations can occur, and contact ismade and broken several times before stabilizing. Counting all these signals would yield too high afrequency. The debounce circuit solves this problem by ignoring rising edges not preceded by a sustained
low signal. The sustain interval can be set in software to 0, 0.6, 2.5, or 10 ms for each channel.
Debouncing may be disabled (0 ms) for clean, high-frequency signals. Long debounce times will limit
high-frequency response (e.g., a 10 ms debounce will limit the frequency to about 100 Hz). In general, use“0” (debounce disabled) for clean, high-frequency signals; increase the debounce as needed for noisy, lowfrequency signals from switches and relays.

DBK55, pg. 4987693

DBK Option Cards and Modules

The figure shows the effect of 10 ms debouncing on a noisy signal. To be counted, a rising edge must be
preceded by a low sustained for at least 10 ms without any other edges. Rising edges a and f are counted
because they are preceded by low signal levels sustained for at least 10 ms (the debounce time). All otherrising edges (b, c, d, and e) are ignored. Any falling edge makes (or keeps) the debounced output low,
regardless of preceding edges. Thus, the DBK55 can detect short pulses even with debouncing.

Frequency Measurement
After debouncing, the signal’s frequency is ready to be measured. Frequencies are measured to 12-bit
accuracy between a minimum frequency (Fmin) and maximum frequency (Fmax). This frequency range canbe programmed individually for each channel. The limitations on F min and Fmax are:•

The frequency range must be within 0 to 1 MHz.

••

Fmax - Fmin must be at least 1 Hz.
Fmax / Fmin must be at least 100/99 (1.010101).

Based on F min and Fmax , the DBK55 measures the frequency by counting input cycles during a variable
time interval. The length of the interval depends on the difference between Fmin and Fmax .
•For a wide range (when Fmin and Fmax are far apart), each bit of the 12-bit result represents alarge frequency change and can be measured quickly.

•

For a narrow range (when Fmin and Fmax are close together), each bit of the 12-bit result
represents a small frequency change and takes longer to measure.

The following equation determines the time interval needed to measure a frequency:
Minimum Measurement Period (sec) = (4096 x 0.5 µs) [Fmax/(Fmax - Fmin)]In this equation: 4096 derives from 12-bit precision; 0.5 µs is the resolution of the DBK55’s timing
circuits; and Fmax / (Fmax - Fmin) is the ratio the measurement time must be increased to achieve 12-bit
accuracy over the selected range.
To see how the measurement period varies, consider two examples:•

To measure frequencies from 59 to 61 Hz, the measurement period is at least
4096 x 0.5 µs x 61/2 = 62.5 ms, or about 16 measurements per second.

•

To measure frequencies from 1 to 61 Hz, the measurement period is at least
4096 x 0.5 µs x 61/60 = 2.1 ms. Note that as the DBK55 only measures frequency once per
cycle, it would take from 1 to 61 measurements per second.

Thus, measuring frequencies over a narrow range takes longer than over a wide range as the ratio of
Fmax/(Fmax - Fmin). The actual measurement time is the sum of several items: the minimum measurement
period (from the equation above), the actual input period, and a variable processing time of 0 to 4 ms.
Note: If the Sequence Rep Rate is set faster than the measurement rate, multiple readings of thesame measurement will occur.
After the frequency (F) is measured to the required accuracy, it is scaled to a 12-bit number (D) for use by
the Digital to Analog Converter (DAC). This 12-bit number is determined by the formula:D = 4096 [(F - Fmin) / (Fmax - Fmin)]; where: 0 < DAC < 4096
DBK Option Cards and Modules

987693

DBK55, pg. 5

If the measured frequency is Fmin, then the scaled result is 0. If the measured frequency were Fmax, then thescaled result would be 4096 but is limited to 4095. Measured frequencies below Fmin are scaled as 0;
frequencies above Fmax are scaled as 4095. The highest frequency that produces an accurate result is theone that converts to a DAC value of 4095; that is, Fmin + 4095/4096 (Fmax - Fmin) which is the same as
Fmax - 1/4096 (Fmax - Fmin).

Digital-to-Analog Conversion
The 12-bit scaled result of the frequency measurement is stored in a DAC to be read by the data acquisition
system. The DBK55 makes use of two DACs. The first DAC is shared by channels 0 through 3 and thesecond by channels 4 through 7. Each time the LogBook or Daq device addresses a different DBK55
channel, the associated DAC supplies the corresponding voltage (Vout) according to the formula:
Vout = 10.0 (D/4096) - 5.0 V
Since DAC values (D) range from 0 to 4095, DBK55 output voltages range from -5.0000 to +4.9976 V.
Calibration for the DBK55 is automatic. When the DBK55 is initialized through software, its gain andoffset errors are measured. The output circuits are then adjusted so the LogBook or Daq device
measurements correspond to the DAC settings. The DBK55’s software-adjustable gain and offset cancorrect for small errors in the DBK55 or the LogBook or Daq device. This automatic calibration
eliminates the periodic need for manual calibration.

Hardware Setup
CAUTION
DBK55 modules must be configured before connecting them to inputs and outputs.
Failure to do so could result in damage to equipment.
Hardware-related steps for setting up DBK55 include:••••

Configuring the DBK55 for the application
Configuring the Daq device to which the DBK55 is being connected toConnecting the input cables to sensors
Connecting the module’s output cable to a Daq device or LogBook.

Configuring the DBK55 Module
Unless the factory default settings are going to be used, several jumpers and one switch must be set on the
DBK55 module to match both the system setup and the signal-conditioning requirements. Each channel
can have its own individual hardware and software settings.
The default settings are:
• Input Circuit – set to Analog• Attenuation – set to Enabled (less sensitive)• Low Pass Filter – set to 100 kHz

The following table indicates the possible settings of each jumper and includes an illustration to facilitate
the location of jumpers. More detailed information concerning jumper settings immediately follows thetable.

DBK55, pg. 6987693

DBK Option Cards and Modules

DBK55 On-board Jumper Configurations
Configuration

Jumpers

ChannelJP3 and JP4

CH 0• The default is Analog Input;

JP23 and JP24

CH 1

Pins 1 and 2 connected for
two associated jumpers.

JP43 and JP44

CH 2

• For Digital Input mode; pins

JP63 and JP64

CH 3

JP103 and JP104

CH 4

JP123 and JP124

CH 5

JP143 and JP144

CH 6

JP163 and JP164

CH 7

Attenuation Selection, pg. 8

JP1

CH 0

• The default is Attenuation

JP21

CH 1

Enabled (reduced
sensitivity). Pins 1 and 2
are connected.

JP41

CH 2

JP61

CH 3

JP101

CH 4

JP121

CH 5

JP141

CH 6

JP161

CH 7

Low Pass Filter Selection, pg. 8

JP2

CH 0

• The default LPF is 100 kHz.

JP22

CH 1

Pins 1 and 2 are connected.

JP42

CH 2

JP62

CH 3

JP102

CH 4

JP122

CH 5

JP142

CH 6

JP162

CH 7

Input Circuit Selection, pg. 8

2 and 3 are connected forthe two associated jumpers.

• For Full Sensitivity(Attenuation Disabled) pins
2 and 3 are connected.

• For an LPF of 300 Hz, pins
2 and 3 are connected.

• For an LPF of 30 Hz, pins 3
and 4 are connected.

Jumper Locations
DBK Option Cards and Modules

987693

Selected Functions

Analog(Default)

Digital* Two jumpers are required to set Analog
or Digital. For example, JP3 and JP4,
which are at the input and output ends ofthe circuit, respectively.

Attenuation
Enabled(Default)

Full
Sensitivity

Partial Board, Not Drawn to Scale
DBK55, pg. 7

Input Circuit Selection: Analog or Digital
Each input channel can be set for the analog (default) or digital circuit. Two jumpers must be set for eachchannel. These are listed in the preceding table, along with the associated channels.
Refer to the previous figure and table; then select the input circuit for each input channel as follows:1.

Determine the best circuit type for each channel.
• The digital input circuit works best for DC-coupled signals where the low level is less than
0.5 V and the high level is above 2.5 V and the voltage does not exceed ±15 V. By using apull-up resistor, switches and relays can create the signal. Frequencies can be as high as
960 kHz. The digital input circuit does not attenuate or filter the input signal.

•

The analog input circuit is AC-coupled and is sensitive to signals from 100 mV to 84 V p-p.
It also provides attenuation and low-pass filtering to reduce the effects of noise.

2.

Position each channel’s circuit jumpers (2 jumpers per channel) for analog or digital.

3.

Verify that both jumpers for a channel are set the same, i.e., both set to pins 1 and 2 for Analog, orboth set to pins 2 and 3 for Digital.

Attenuation Selection (Analog Input Circuit Only)
When measuring strong analog signals, the attenuator can reduce the input sensitivity and the effects ofnoise. If enabled, the attenuator reduces the input sensitivity by a factor of 50.
Refer to the previous figure and table; then set the attenuation for each channel as follows:1.

Decide whether or not you want attenuation for a given channel. Attenuation enabled, which
reduces sensitivity, is the default setting.
• Use attenuation (reduced sensitivity) if the input signal’s peak level exceeds 1 V.
• Disable attenuation (full sensitivity) if the input signal’s peak level is less than 1 V.

2.

For attenuation, position the associated jumper across pins 1 and 2. To disable attenuation (fullsensitivity), position the jumper across pins 2 and 3.

3.

Verify the jumper position for each input channel.

Low-Pass Filter Selection (Analog Input Circuit Only)
The low-pass filter removes high-frequency noise that would otherwise have the DBK55 detecting a higher
frequency than desired. To set the low-pass filter:

DBK55, pg. 8

1.

Determine the highest frequency you expect to measure on each input channel.

2.

Select the next higher cutoff frequency (30 Hz, 300 Hz, or 100 kHz) for each corresponding channel.
Verify that the DBK55’s sensitivity will accommodate the expected input signal strength. Page 3
includes a graph of typical sine-wave sensitivity (peak-to-peak voltage) verses frequency (Hz).

3.

Refer to the previous figure and table; then set the associated jumpers for the desired low-pass filter
selection.

987693

DBK Option Cards and Modules

Address Configuration via Rear Panel DIP Switch
You can connect 1 or 2 DBK55 modules to a single main channel on the primary data acquisition device.
Thus, a 16-channel LogBook or Daq device can support up to 32 DBK55 modules. Since each module has
8 input channels, a fully populated system can use 256 input sensors (32 modules x 8 channels per
module).
To keep the large number of inputs organized, each DBK55 module is given a unique address via its DIP
switch, S1[located on the rear panel].

CAUTION
Each DBK55 must be configured before connecting the module to inputs and outputs.
In addition, adjustment of the channel address must only be performed when thesystem’s power is OFF. Failure to do so may result in equipment damage.
S1’s four leftmost micro-switches are used to set the module’s channel address in binary. Set the microswitches to the desired address only after ensuring that the system power is OFF. Several example address
settings are provided below. Other settings can be easily derived.
Each DBK55 module in the system must have a unique channel address for the primarydata acquisition device. Valid addresses are 0 to 15. Note that two modules can have asetting for the same primary channel, for example, two modules could be set to channel
0; as long as one module is set to “L” to indicate the lower sub-channels 0-7 and theother is set to “U” to indicate the upper sub-channels of 8-15. Examples of various
settings follow.
Primary Acquisition Device Channel 0
DBK55 Lower Sub-Channels 0-7
Channel 0 / Lower

The four leftmost micro-switches are set to “0” (Open). This sets the unit to
primary acquisition device Channel 0. The rightmost switch is at “L,”setting the module to the “lower” DBK55 sub-channels (0 through 7).
Note: If connecting a second module to primary device Channel 0, the U/L
switch for that module would be set to “U” for sub-channels 8 thru 15.
Primary Acquisition Device Channel 5
DBK55 Lower Sub-Channels 0-7

Channel 5 / Lower

The micro-switches for binary 4 and binary 1 are closed. This sets the unit to
primary acquisition device Channel5. The rightmost switch is at “L,” setting
the module to the “lower” DBK55 sub-channels (0 through 7).
Primary Acquisition Device Channel 15
DBK55 Lower Sub-Channels 0-7

Channel 15 / Lower

The micro-switches for binary 8, 4, 2, and 1 are closed, thus setting thechannel to “15” (8 + 4 + 2 + 1) for the primary acquisition device. The
rightmost switch is at “L,” setting the module to the “lower” DBK55 subchannels(0 through 7).
Primary Acquisition Device Channel 2
DBK55 Upper Sub-Channels 8-15

Channel 2 / Upper

DBK Option Cards and Modules

The micro-switch for binary 2 is closed, thus setting the channel to “2” for the
primary acquisition device. The rightmost switch is at “U,” setting the module
to the “upper” DBK55 sub-channels (8 through 15).

987693

DBK55, pg. 9

Configuring the Primary Data Acquisition Device
DaqBook/100 Series & /200 Series and DaqBoard [ISA type] Configuration
Several setup steps of DaqBook/100 Series & /200 Series devices
and DaqBoards [ISA type] are required to use DBK55
modules in a system.
1.

If not using auxiliary power, place the JP1 jumper inthe expanded analog mode.

Note: This default position is necessary to power theinterface circuitry of the DBK42 via the internal±15 VDC power supply. If using auxiliary power(DBK32A/33), you must remove both JP1 jumpers(refer to the Section Power Requirements in the
document module DBK Basics, in regard to
calculating system power requirements).

CAUTION
When using the SSH output, do not use an external voltage reference for DAC1.
Applying an external voltage reference for DAC1, when using the SSH output, will
result in equipment damage due to a conflict on P1, pin #26.
2.

Place the JP2 jumper in the SSH position (See previous CAUTION).

3.

For DaqBook/100, /112 and /120 only, place JP3 jumpers in bipolar mode.

4.

For DaqBook/100, /112 and /120 only, place JP4 jumpers in single-ended mode.

DaqBook/2000 Series & DaqBoard/2000 Series
No jumper configurations are required on the DaqBook/2000 series and DaqBoard/2000 series devices inregard to connecting a DBK55.
LogBooks
No jumper configurations are required on LogBook devices in regard to connecting a DBK55.

CE ComplianceIf your data acquisition system needs to comply with CE standards, the DBK55 must be connected to the
LogBook or Daq device by a CA-143-x cable.
Note that in the presence of 3 V/m RF fields, the following conditions must exist in order to meet CE
requirements:•

500 mVpp signals are required to maintain 0.1% accuracy.

•

Metal shells of the BNC connectors must be directly connected to the chassis ground in orderto maintain 100 mV sensitivity and 0.1% accuracy.

•

The host computer must be properly grounded.

•

The host computer and peripheral equipment must be CE compliant.
Reference Notes: If your data acquisition system needs to comply with CE standards,
refer to the CE Compliance section of Signal Management chapter.

DBK55, pg. 10987693

DBK Option Cards and Modules

Connecting the DBK55 to Signals and to the Primary Data Acquisition Device
You can connect the DBK55 module to your primary data acquisition device and to its signal inputs after
you have completed the following:•••

set the DBK55 module’s addressconfigured the DBK55 on a channel-by-channel basis for the application
configured the primary data acquisition device, if applicable

You can connect up to eight sensors to one DBK55, i.e., one per BNC. A CA-37-x (or CA-131-x) cable isused to connect the module to a LogBook or Daq device via the module’s DB37 connector (P1).

WARNING
Electric shock hazard! Do not exceed a sensor input of 30 Vrms (42 Vpeak, 84 Vp-p)
for analog or ±15 Volts for digital. Exceeding these values may present an electric
shock hazard that could possibly result in injury or death, in addition to DBK55
damage.
Connect the DBK55 module as follows. If your system needs to be CE Compliant, be sure to read thepreceding CE Compliance section prior to connecting the DBK55.
1.

Connect each sensor’s BNC connector to a mating connector on the DBK55 module
Label each sensor with its associated channel/sub-channel information.

2.

3.

For a single DBK55 module, connect one end of the P1 cable to the module’s male
DB37 output connector.
•

For DaqBook applications - use a CA-37-1 cable.

•

For DaqBoard/2000 Series or /2000c Series boards - use a CA-37-1 with a
DBK200 Series adapter.

•

For DaqBoard [ISA type] boards - use a CA-131-1 cable.

Connect the free end of the cable to the P1 port of the LogBook or Daq device. For multiple DBK55
modules, use a CA-37-x (or CA-131-x) cable to daisy-chain several modules or an expansion
module. For example, three DBK55s could be connected to a LogBook or a Daq device with via a
CA-37-3 cable.

Note: For longer cable runs, use a CA-113 to add 6 ft of cable length where needed.

Software Setup
LogView does not include the means to directly select DBK55. However, since a single
DBK55 has the functionality of two DBK7 cards we can still use a DBK55 with
LogBook. To do this, select DBK7 in LogView. This will recognize the DBK55, but will
identify it as a DBK7. Next do one of the following, as applicable:(a) If the DBK55 is set to the L sub-address, Select DBK7 (0) and DBK7 (1)(b) If the DBK55 is set to the H sub-address, Select DBK7 (2) and DBK7 (3)Reference Notes:
o DaqView users - Refer to Chapter 3, DBK Setup in DaqView.
o LogView users - Refer to Chapter 4, DBK Setup in LogView. See above note.

DBK Option Cards and Modules

987693

DBK55, pg. 11

Specifications - DBK55
Name/Function: 8-Channel Frequency-to-Voltage Input Card
Input Channels per Module: 8
Maximum Modules per System: 32
Maximum Channels per System: 256
Input Connector: 1 BNC connector per channel
Connector: DB37 male, mates with P1
Frequency Ranges: (programmable) 0 Hz to 960 kHz
Output Voltage Range: -5 V to +5 V
Debounce Delays: (software selectable) 0, 0.6, 2.5, 10 ms
Measurement Rate: up to 500 per second per channel, 1000 per second total
Accuracy: 0.1%
Power Required: 840 mW

Analog Input
Low-level:
50 mV typical (100 mV max) p-p sine wave @ 10 Hz to 100 kHz
Any edge of 50 (100 max) mV amplitude and 5 V/s rate.
Input impedance: AC-coupled (0.33 µF), in series w/ 20 KΩ to ground.
15 mV hysteresis.
High-level:0.75 V typical (1.25 V max) p-p sine wave @ 10 Hz to 100 kHz
Any edge of 0.75 V (1.25 V max) amplitude and 50 V/s rate.
Input impedance: AC-coupled (0.33 µF), in series w/ 20 KΩ to ground.
250 mV hysteresis.
Maximum Input Voltage: 30 Vrms (84 Vp-p)
Low-Pass Filters: (hardware selectable) 30 Hz, 300 Hz, 100 kHz, single pole

Digital Input
TTL-Level: 0.001 to 960 kHz.
Input Impedance: 27 KΩ pull-up to +5 V || 50 pF
V Low (“0”): 0.8 V typ, 0.5 V min
V High (“1”): 1.6 V typ, 2.1 V max
Hysteresis: 400 mV min
Pulse Width (high or low): 520 nsec min.
Maximum Input Voltage: -15 V to +15 V

DBK55, pg. 12987693

DBK Option Cards and Modules