How do I measure?

Signal Input and Conditioning for Black Lab

Black Lab specific information on how to measure voltage, temperature, strain gauges, mA signals, force sensors, etc.

Background

This document was prepared to describe how to measure different input signals types and sensors with the Black Lab. The tables shown below lists most of the popular sensor types used today and describe how to prepare each sensor for measurement and whether additional signal conditioning will be needed.  Note in general that the Black Lab will measure almost any sensor output with a voltage signal from microvolts to 10 volts using the Black Lab gain choices (1x,10x,100x,1000x). Once the signals are measured by the Black Lab and made available as volts, the signal can be further scaled through linear and polynomial equations.  An auto zeroing feature is also available to automatically zero sensor output signals before each test.

Analog Sensor Types

Analog Sensor Type	Direct Input To Black Lab	Signal Conditioning Recommended	Notes
Voltage			* Use isolation when the input voltage exceeds the common mode input voltage.
Volts DC	Yes *	No
Millivolts DC	Yes *	No	Consider using Black Lab gains of 10,100, or 1000.
Isolated volts DC	No *	Yes	Use isolation to protect the Black Lab and testing computer against potentially harmful voltage transients, large ground differences, and noise.
Volts AC	Yes *	Yes	AC voltages can be measured by the Black Lab provided the sample rate is correctly set. For best results, consider signal conditioning with isolation.
High impedance output	No	Yes	For best results, the Black Lab should use external signal conditioning (that is usually integral to the sensing device)

Analog Sensor Type	Direct Input To Black Lab	Signal Conditioning Recommended	Notes
Current			* To measure current, a shunt resistor is needed across the Black Lab input to convert current to voltage.
amps	Yes *	(See note 1)	A low resistance shunt with a Watt rating sufficient to accommodate the current expected with a safety margin added.
milliamps	Yes *	? (See note 2)	A large ohmic shunt resistor is needed to convert the mA signal to voltage.
2 or 4 wire 4-20 mA transmitter	Yes *	No (See note 2)	Consider using CIM 3 with the 24V output to provide loop power.
Clamp on probe, Hall effect, or wire loop	Yes	Yes (See Note 3.)

Analog Sensor Type	Direct Input To Black Lab	Signal Conditioning Recommended	Notes
Bridge / Resistance			* For all the sensor types listed in this section, consider using CIM 3 with the variable 1.2 to 10 volt regulated excitation for use with a direct input connection.
Load cell / Force sensor	Yes *	No	The Black Lab can accommodate a load cell output directly.  Consider adding signal conditioning when additional filtering or excitation is needed.
Strain gauge	Yes *	No	Same note as Load cell.  A bridge completion circuit may be needed.
Potentiometer, lanyards, or other resistive devices	Yes *	No

Analog Sensor Type	Direct Input To Black Lab	Signal Conditioning Recommended	Notes
Temperature
Thermocouple	Yes	No	The Black Lab can accommodate thermocouple inputs directly.  Consider additional signal conditioning only when the TC needs voltage isolation or noise reduction.
NTC thermistor	Yes	No	Consider using CIM 3 with the variable 1.2 to 10 volt regulated excitation
RTD	No	Yes	For best results, the Black Lab should use external signal conditioning for excitation and linearization.

Analog Sensor Type	Direct Input To Black Lab	Signal Conditioning Recommended	Notes
Amplified			Devices in this section are assumed to have amplified sensors that have a built in or external signal conditioning board, provide a signal output in volts, demodulate and filter the sensor signal, and do not require linearization.  See Note 4.
Pressure	Yes	No	Voltage or current outputs can be read by the Black Lab
Level, Flow	Yes	No
pH, conductivity	Yes	No
LVDT	Yes	No	DC voltage output proportional to position.
Accelerometer	Yes	No
Position	Yes	No	DC voltage output proportional to position.

Analog Sensor Type	Direct Input To Black Lab	Signal Conditioning Recommended	Notes
Frequency			Note signals in this section with a TTL (or higher) voltage with a digital output can be accommodated directly with the Frequency digital input on the Black Lab.
TTL output, encoder, tachometer	No	Yes	Consider using an external Frequency to Voltage (F/V) converter.

Notes:

1. When measuring current, check to see that common mode voltage is not exceeded on the Black Lab input when using the Black Lab in a grounded situation.  If so, consider isolating the signal.Isolation current signals may be the safest worry free option when measuring signals in an industrial environment.
2. A 250 ohm resistor is used typically.Beware of loop compliance with power supply voltages less than 24V or larger shunt resistor values.
3. The Black Lab can read the output of a Clamp on probe (or a Hall Effect or wire loop) and provide a gross indication of current flow and relative strength.  For more quantitative information like true RMS power measurement, for example, consider using a Clamp on meter with an analog output to connect to the Black Lab.
4. The Black Lab can provide the voltages (12 and 24 volts) needed to power these transducers.  The 12 and 24 volts provided by Black Lab are regulated but not excitation grade.

Digital Sensor Types

Digital Sensor Type	Direct Input To Black Lab	Signal Conditioning Recommended	Notes
Passive Switch and Relay Contacts			See Note 1
Proximity Switches	Yes	No
Photoelectric Switches	Yes	No
Limit Switches	Yes	No
Pushbuttons	Yes	No
Relays	Yes	No	Open set of contacts available
Pressure, Vacuum and Differential Switches	Yes	No
Powered Devices			See Note 2
Relays	Yes	No	No open set of contacts available.
Motors	Yes	No
Solenoids	Yes	No
Indicator Lamps	Yes	No
TTL Output	Yes	No
Frequency			See Note 3
TTL output, encoder, tachometer	Yes	No

Notes:

1. Because these signals do not generally have a voltage output to drive the Black Lab opto-isolated inputs, an excitation source must be provided.  If a 5-12 volt output signal is not available from these devices (from a relay contact or coil for example), then use the 5 volt excitation voltage provided by the Black Lab.
2. Since these signals provide a voltage output, they can be used to drive the Black Lab opto-isolated digital inputs.  Make sure that each source can drive approximately 2 mA of current.In addition, limit the input current to 10 mA or damage can result.  Active low outputs (open collector) can also be accommodated.  Any AC voltage signals should be rectified with a filter capacitor or use a digital input conditioning module.
3. Note signals in this section with a TTL voltage (voltage up to 12V) with a digital output can be accommodated directly with the Frequency digital input on the Black Lab.

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