Can I Connect my own Tachometer or Strobe to the Tach Input of my vb Portable Instrument?

The information provided is for help with Commtest Instruments products:

vbSeries® instruments

QUESTION

Can I connect my own tachometer or strobe to the tach input of my vb portable instrument?

ANSWER

Yes you can, provided your strobe has a digital output (e.g. TTL or switch). The following strobe cable can be purchased directly from CTC:

CB110-C395-010-C302
1/8"" Mono Plug to 4 Pin LEMO, 10 ft, wired for TTL signal, suits vb5, 6, 7, 8, Balancer, Balancer+ (e.g. suits Monarch Nova-Strobe range)

And the following BNC cables can be purchased from your Commtest rep (see www.commtest.com/content/products/vbSeries/accessories.aspx):

TTL70259 TTL Tachometer Cable (vbX)
BNC Plug (male with spinning collar) to 4 Pin LEMO, 2 m, wired for TTL signal, suits vb5, 6, 7, 8, Balancer, Balancer+

KEY70258 Keyphasor Tachometer Cable (vbX)
BNC Plug (male with spinning collar) to 4 Pin LEMO, 2 m, wired for Keyphasor signal, suits vb6, 7, 8, Balancer+

CABK0108 Keyphasor Tachometer Cable (vbX000)
BNC Plug (male with spinning collar) to Switchcraft, 2 m, wired for Keyphasor signal, suits vb1000, 2000, 3000, 1000b

Making your own cable

For earlier vb instruments (vb1000...vb3000), or for tachs and strobes with non-TTL outputs or different connectors to those above, you must obtain the cable and connectors and wire them up yourself. We do not supply the cables because of the very large variety of connectors fitted on strobes and the differing wiring required.

Sourcing the connector and cable

vbX instruments, such as the vb7, use a LEMO connector for the tachometer input. This connector can be obtained by purchasing a "vb7 Laser Tach cable" from your local Commtest reseller. The connector at the laser tach end should be removed and re-wired for your strobe as below.

vb1000, vb2000 & vb3000 instrument's use a Switchcraft connector, model TA4F for the tachometer input. This can be obtained by purchasing a "Tachometer Extension Cable (CBLE0028)" from your local Commtest reseller. This will provide you with the TA4F connector and cable; you will only need to replace the connector at the strobe end.

Alternatively, the TA4F connector can be obtained from some electronics components catalogues, for example:

Allied Electronics

part number 932-1202

Ph:1-800-433- 5700 or (1-817) 595-3500

Wiring Information

The pins of the tach connector are connected internally to the vb instrument as follows (applies to both vbX000 and vbX instruments):

Tach + Positive tach input to vb instrument (isolated).
Ground
Tach - Return line from tach input (isolated).
Supply From the main vb battery; 6 to 9 V; only on while measuring; limited to 100 mA.

Here is a view of the connector from the outside (your connector is numbered but this numbering is very small).

lemo_wiring

Ascertaining your Tachometer's Digital Output

Now you need to find out what kind of digital output your tach provides. If you don't know, use the instructions below to test if it uses the TTL option first. If this doesn't work try the Switch option.

TTL output

(strobe drives its output to, say, 5 V. e.g. Monarch strobes)

Connect the Positive (Output) from the strobe to pin 1 of the tach connector.
Connect the Negative (Ground) from the strobe to pin 3 of the tach connector.
Leave the other two pins of the Switchcraft connector unconnected.
Note: You will not do any damage by swapping Positive and Negative, but the vb instrument will not detect the strobe pulses.

Switch output

(strobe pulls output down to Ground but does not provide an output voltage)

Connect Switchcraft connector pin 4 back to tach connector pin 1 (Supply+).
Connect the Positive (Output) from the strobe to pin 3 (Tach-) of the tach connector.
Connect the Negative (Ground) from the strobe to pin 2 (Gnd) of the tach connector.
Note: This is the wiring that should be used if using a simple make/break switch output. The laser tach cables from Commtest are pre-wired in this configuration, with the link between pins 1 & 4.

Test if the Tachometer is Working

The exact keys you need to press will vary depending on which version of the instrument firmware you are using. Use one of the bulleted instructions below to take a measurement.

From the vbX Main Menu select Measure>Tachometer Display.

From the vbX000 Main Menu select Measure>Tach Display then press START/STOP.

From the vb1000b Main Menu select Balancing>Trial readings>Initial Reading and press Enter.

FAQ ID: 11678 Last Reviewed: 23 July 2008